## How many digits of Pi do you know?

For the discussion of math. Duh.

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smw543
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### Re: How many digits of Pi do you know?

I thought I knew 24 digits, but I missed the 13th. I guess that technically makes it twelve, though I got the rest of 14-24 correct. (In my defense, the only advanced math I've done in over a year has been for science classes, and we always get to use our calculators...I'm so ashamed )

But more importantly, this is my π(314th) post!
Spoiler:
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a Person
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### Re: How many digits of Pi do you know?

OK, so here's my "rhythm" for pi:
3.14159 26535 8979 3238 46264 33832 7 9502884 197169 3993 751 058 2 097 4944 5923078 1640628 6208998 6280348 25342 11 706798 2148 08651 32823 0664 5505 8223 172 535

Kurushimi
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### Re: How many digits of Pi do you know?

3.14159 26535 897 93238462 64338327 9

miles
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### Re: How many digits of Pi do you know?

3. 1415926535 8979323846 2643383279 5028841971 6939937510 5820974944 5923078164 0628620899 8628034825 3421170679 8214808651 3282306647 0938446095
not fair though since i reviewed my pi after seeing this, memorized in sets of 10 like phone numbers

MarcyMarc
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### Re: How many digits of Pi do you know?

bored in programming class, ms calc only has thirty some digits

3.14159 26535 8979 323 846264 3383 2795

*897 is the 1st 3 digits of my phone #

*275 (from 2795) is one of my friend's 1st three digits
marcYɔɹɐɯ

anna95
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### Re: How many digits of Pi do you know?

i learnt 21 digits of pi just reading a poster in my maths classroom, but then i learnt another 3

3.14159265358979323846264

thicknavyrain
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### Re: How many digits of Pi do you know?

3.14159265358979

I used to know it to only 3.1415926535 but then I realised that wasn't properly rounded so I kept going until I found a digit with a digit lower than 5 after it, (hence the extra 8979).
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fwlbg
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### Re: How many digits of Pi do you know?

I remember it more easily in binary (to 64 bi-mal (?) places), even though it's just "1"s and "0"s, and you need more binary digits to approximate pi to the same level of accuracy (or is it precision?) than with decimal digits:

11 . 001001 0000 111111 01101 0101 00010001 0000 101101 00011 0000 1000 1101 0011

Srsly.

Maybe I should learn it to many places in hexadecimal instead, then it would be more accurate (precise?) than with the same amount of decimal digits.

potatoman
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### Re: How many digits of Pi do you know?

I know about 200ish. 3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679 8214808651328230664709384460955058223172535940812848111745028410270193852111055964462294895493038196... I used to know 400 but I forgot a few.

Yakk
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### Re: How many digits of Pi do you know?

thicknavyrain wrote:3.14159265358979

I used to know it to only 3.1415926535 but then I realised that wasn't properly rounded so I kept going until I found a digit with a digit lower than 5 after it, (hence the extra 8979).

But what digit lower than 5 is it? Huh?
One of the painful things about our time is that those who feel certainty are stupid, and those with any imagination and understanding are filled with doubt and indecision - BR

Last edited by JHVH on Fri Oct 23, 4004 BCE 6:17 pm, edited 6 times in total.

brakos82
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### Re: How many digits of Pi do you know?

I am Brakos, and I may or may not approve this message.

John_S
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### Re: How many digits of Pi do you know?

3.1415926535897932384626433

25. (26, if you count the 3)

cpp789
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### Re: How many digits of Pi do you know?

I know 2^8 (256) digits after the decimal point. I've found that if I run through them in my mind at a constant rate, it takes almost exactly 60 seconds (with a standard deviation of 5). As long as I'm doing a fairly repetitive and thoughtless activity, it works pretty well as a timer.

The EGE
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### Re: How many digits of Pi do you know?

3.14159265358979323846264338327950288419716939937510....

50 digits past the decimal point. I could do 100 for a while, and at one point I knew 250 for a few days. Then I had to say it in spanish for a competition... mental number conversion ftw.

*goes out to memorize a bunch more*
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WazirKnightBishop
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### Re: How many digits of Pi do you know?

I could do all the way up to this far: [1 double linebreak per 5 lines]

3.14159
26535897
93238462
643383279
50288419
71693993

75105820
97494459
23078164
06286208
99862803

48253421
17067982
01808651
32823066
47083844

60955058
22317253
59408128
48111745...

19 × 8 + 1 - 2 = 151 d. p.

To be honest, I got hold of a song that just starts 3.14159... and goes on and on. Once you get the rhythm (8 or 9 digits per line) it's quick.
~~~~

The EGE
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### Re: How many digits of Pi do you know?

3.1415926535897932384626433832795028841971693993751058209749445923078164...

70 now.

I tend to memorize in blocks of 5, mostly. The first 20 are in pairs, though, and 61-70 i think 592307 8164.
sillybear25 wrote:But it's NPH, so it's creepy in the best possible way.

capncanuck
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### Re: How many digits of Pi do you know?

Personally: 3.14159265358979323846264338327950288419716939937510582097494459230781

Pi Song, the song without a chorus

And an old web page I found: http://www.albanyconsort.com/pi/

Gaydar2000SE
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### Re: How many digits of Pi do you know?

I know all digits, '10', but I always write π in a positional numeral system with a radix of π to cheat. I have Greek installed so I can be awesome, και συ, τεκνον;

Besides, the most efficient algorithms to compute π always return the string in hexadecimal, and numbers always look 'simpler' in that, I guess it's ultimately better than decimal. It's also 2^2^2 and all...
^ :/

gmalivuk
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### Re: How many digits of Pi do you know?

Yes brilliant and hilarious and you're only about the 40th person to point out that you've memorized the digit of Pi in base Pi ha ha ha.
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Gaydar2000SE
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### Re: How many digits of Pi do you know?

Oh well, I can probably come back with some ad hominem saying that you're then at least the 10^40th person to point out that's it done before but I'll go cry I guess, Scotty, hand me the razor.

edit: I shall try to be slightly more original by memorizing it in an ln(-1)/i base next time.
^ :/

Dew_N_O
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### Re: How many digits of Pi do you know?

I know all the digits of pi:

10.

See, I use a base of digits that makes it so that when you start to talk about things, the things change right in front of you.

I use a base of digits that makes people suffer that shouldn't.

Oh wait that happens without a base or any good reason.

TheGuyWithTheHat
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### Re: How many digits of Pi do you know?

64. I also like the number 64 because it's one of the "flash memory numbers" and it's even and a multiple of two, plus half 64 is 32 and that's my lucky/favorite number.
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Orkimond
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### Re: How many digits of Pi do you know?

I used to know 120 digits, learnt it for a school comp, but now I only know 60 or so.

Here's a question, does pi contain, by the nature of it's irrationality, a string of arbitrary length of the same digit within pi?

PM 2Ring
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### Re: How many digits of Pi do you know?

Orkimond wrote:I used to know 120 digits, learnt it for a school comp, but now I only know 60 or so.

Here's a question, does pi contain, by the nature of it's irrationality, a string of arbitrary length of the same digit within pi?

Possibly, but we don't know for certain. http://en.wikipedia.org/wiki/Normal_number
Wikipedia wrote:In mathematics, a normal number is a real number whose digits in every base show a uniform distribution, with all digits being equally likely, all pairs of digits equally likely, all triplets of digits equally likely, etc.

While a general proof can be given that almost all numbers are normal, this proof is not constructive and only very few concrete numbers have been shown to be normal. It is for instance widely believed that the numbers √2, π, and e are normal, but a proof remains elusive.

Piogre
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### Re: How many digits of Pi do you know?

I've known 70 digits since the 6th grade:

3.1415926535897932384626433832795028841971693993751058209749445923078164

MidsizeBlowfish
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### Re: How many digits of Pi do you know?

3.14159

Six. If I wanted to know more, I'd ask a computer.

Kurushimi
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### Re: How many digits of Pi do you know?

Does anyone know any good programs for memorizing digits of pi?

mimizu
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### Re: How many digits of Pi do you know?

3.14 159 2653 58979 3238 462 643 383 279 50288 41...

And then I messed.

minno
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### Re: How many digits of Pi do you know?

Posted without looking at any other posts besides the opening one:

3.14159265358979323. 17 digits after the decimal point.

The only time I actively tried to memorize them was on pi day in 8th grade (march 14, 3/14). I used to know about 10 digits after that, but it's been 3 years.
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RabidAltruism
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### Re: How many digits of Pi do you know?

3.14159265 .. and then I can never remember whether a 3 or a 4 follows next.

I thought I was doing pretty well at that length! Seems I've got a long way to go on my pi mnemonics is I want to be competitive 'round here.
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achan1058
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### Re: How many digits of Pi do you know?

3.141592, despite the fact that I am going to be a mathematician. (a grad student currently) As said above, if I want more digits I get the computer.

Scip
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### Re: How many digits of Pi do you know?

3.1415926535987932384626433 - 21, including the 3. I used to know 30 digits after the decimal point for pi day in 9th grade. When I'm bored nowadays, sometimes I'll just memorize a couple more digits from the Windows scienfitic calculator...

PM 2Ring
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### Re: How many digits of Pi do you know?

I just "discovered" an interesting interpolation for the Wallis product formula for pi. I don't think this deserves a new thread, and this seems like a good place for it.

The Wallis product formula is
$\prod_{n=1}^{\infty} \frac{(2n)(2n)}{(2n-1)(2n+1)} = \frac{2}{1} \cdot \frac{2}{3} \cdot \frac{4}{3} \cdot \frac{4}{5} \cdot \frac{6}{5} \cdot \frac{6}{7} \cdot \frac{8}{7} \cdot \frac{8}{9} \cdots = \frac{\pi}{2}$
Note that successive partial products alternate above and below the limit. So it's likely that interpolating between them will give a good pi approximation.

Also note that terms can be grouped into pairs in two ways:
$\frac{n^2}{n^2-1} \mbox{ for even n}$ or
$\frac{n^2-1}{n^2} \mbox{ for odd n}$
The second form is useful because we can divide n² out to give (1-1/n²).

I have found that by calculating upto a term of the form [imath]\frac{2n}{2n-1}[/imath] & interpolating between the last two products, that a much better approximation to pi can be found. Let p be a partial product with the next term being [imath]r = \frac{m+2}{m+1}[/imath]
Next we find a & g, the arithmetic & geometric means respectively of p & pr.
Then a - g is very close to pi - a. So 2a - g is a good pi approximation.

Here's a short bc program that illustrates this technique. Note that m must be even for this to work properly.

Code: Select all

scale=30;m=5000;p=4*m/(m+1);for(i=3;i<m;i+=2)p-=p/(i*i);r=(m+2)/(m+1);p*(1+r-sqrt(r))

The above code yields 3.141592653589793630690807651016

Proof of why this method works will be left as an exercise for the reader.

Of course, this algorithm is rather slow compared to the Arithmetic-Geometric Mean algorithm (and other formulae discovered by Ramanujan), or even some good arctan-based formulae, but apart from one square root most of the arithmetic is very simple.

Elusieum
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### Re: How many digits of Pi do you know?

3.14159265358979323...

18 digits. =)

Spen
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### Re: How many digits of Pi do you know?

3.141592
As Much as I know, a maths teacher in my school knows 65 and a kid in his class is trying to beat that.

BlackSails
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### Re: How many digits of Pi do you know?

MidsizeBlowfish wrote:3.14159

Six. If I wanted to know more, I'd ask a computer.

This.

If I want more, ill ask wolfram|alpha for it. If I really need more and dont have a computer, then just start running the taylor series for arctan

chridd
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### Re: How many digits of Pi do you know?

3.14159 26535 8979 323 846264 3383 279502 884 197169 399 375105 820 974944 59230 78164 06286208 998 6280
86, if I counted right
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Ran4
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### Re: How many digits of Pi do you know?

3 14 159 26 53 5 8979 323 846 26 433
25 digits? Thought I usually stop at 43, to avoid huge rounding errors.

...oh, and one awesome thing I just found out: writing "p" in the windows calculator is actually the same as pressing the pi button. Awesome! (found out when I tried to write "pi").

thicknavyrain
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### Re: How many digits of Pi do you know?

Yakk wrote:
thicknavyrain wrote:3.14159265358979

I used to know it to only 3.1415926535 but then I realised that wasn't properly rounded so I kept going until I found a digit with a digit lower than 5 after it, (hence the extra 8979).

But what digit lower than 5 is it? Huh?

3 and then a 2!

That's as much as I can remember now. Just for you.
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Mavrisa
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### Re: How many digits of Pi do you know?

Gaydar2000SE wrote:edit: I shall try to be slightly more original by memorizing it in an ln(-1)/i base next time.

Ohhh you're a clever one aren't you...

I know someone mentioned phi and e as well and that made me excited, so here goes:

pi:
3.14159265358979323846 soo 21 including the 3.
phi: