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**Dross****Member**- Registered: 2006-08-24
- Posts: 325

This weekend boredom beset me so I went about calculating 1,000,000! (one million factorial).

The number is in a text file, but I can't upload it to geocities (I think it's too large - it'll upload smaller files, but won't give a reason for not uploading this one). The unformatted .txt file is 5.31 MB in size.

Some stats:

1,000,000! has 5,571,271 digits

The last 249,998 digits are zero

In Microsoft Word, with size 10 courier new font, the number takes up 69,641 lines and 1,142 pages

It took 6 hours, 26 minutes and 43 seconds to compute on my machine (2.55 GHz Celeron processor with 1 GB of ram)

The number wasn't calculated by any approximation - sheer brute force was used, so I'm sure it's correct. I'd be happy to send it to someone to put on a website. I'm not sure how large a file I can attach on hotmail though... anybody got any ideas?

Anyway - such are the fruits of my weekend's labour!

*Last edited by Dross (2007-01-14 00:28:32)*

Bad speling makes me [sic]

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**Toast****Real Member**- Registered: 2006-10-08
- Posts: 1,321

Wow, great job Dross! What did you use to calculate it? I'm looking forward to seeing it.

(Courier New is a pretty big font )

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**Devantè****Real Member**- Registered: 2006-07-14
- Posts: 6,400

Sounds interesting.

Maybe you could upload it on rapidshare.

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**Dross****Member**- Registered: 2006-08-24
- Posts: 325

Toast wrote:

What did you use to calculate it?

I wrote a simple program in java. It doesn't just go through one number at a time and update a single variable (i.e. doesn't just compute 1 x 2 x 3 x 4 x 5... straight out) - instead it splits 1,000,000 into sections, so it behaves more like it's doing 1 x 2 x 3 x 4, then 5 x 6 x 7 x 8... and so on, then multiplies the results of all those calculations together. This just makes the program a lot faster because it doesn't have to deal with any ridiculously large numbers until right at the very end of the program when it computes the final result - but it's a crude (uncalculated) optimisation. It could probably be made a lot, lot faster if I took the time to work out how to make it so!

I've never used RapidShare before - I uploaded it and the info on it says "DownloadLink: http://rapidshare.com/files/11657189/1000000Factorial.txt.html" if anybody wants to get at the file.

Don't bother loading it into WordPad - the number has no carriage returns so all the digits go on one line, and it won't let you scroll to the end!

Bad speling makes me [sic]

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**mathsyperson****Moderator**- Registered: 2005-06-22
- Posts: 4,900

I couldn't get at the file. Rapidshare said that I'd reached the download limit for free users, even though I'd never used it before.

I can confirm that 1000000! ends with 249,998 zeroes though. That's the number of factors of 5 that all the numbers from 1 to 1000000 have. (200000 have one, then 40000 have another one, then 8000 have another, 1600 have another, then 320, then 64, then 12, then 2. 200000+40000+8000+1600+320+64+12+2 = 249,988)

Factors of 2 occur more often than factors of 5, and so for every factor of 5, there will always be a factor of 2 that pairs with it. 2x5 = 10, so there are equal amounts of factors of 5 and factors of 10. And for each factor of 10, the number ends with a 0.

I predict (bearing in mind that I couldn't get at the file) that the first number of 1000000! is a 1.

Why did the vector cross the road?

It wanted to be normal.

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**Dross****Member**- Registered: 2006-08-24
- Posts: 325

Alas! The first number is a 3 - it starts off as:

33502795642050604570356757263394648029746124002153075734328879430431840303897445247126830355...

Was 1 a blind guess, or was there rhyme & reason behind it?

Anyway, in a bit I'll post the source code so anybody who wants to can verify that. (I'll comment it so it'll make sense to someone else first )

Bad speling makes me [sic]

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**mathsyperson****Moderator**- Registered: 2005-06-22
- Posts: 4,900

Kind of a bit of both. While you'd expect there to be a 1/9 chance of the first number being a 1, the chance is actually closer to about 30%.

The distribution of all numbers anywhere is not uniform. The probability of any number's first digit being N is given by log(N+1) - log(N). If you look in a newspaper, or any other place that contains numbers, you'll notice that significantly more of them start with 1 than with 9. I'm not entirely sure why that is, but it certainly works.

So, it was kind of an educated blind guess. I had around a 30% chance of being right, but if I was then you'd think that I'd only had 1/9 chance and so it would have seemed slightly more amazing than it was. It was worth a try.

Why did the vector cross the road?

It wanted to be normal.

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**Dross****Member**- Registered: 2006-08-24
- Posts: 325

Here's the source code - if anyone wants to double check it (or reproduce it in any non-money making capacity), feel free.

```
import java.io.*;
import java.math.BigInteger;
public class Tester {
public static void main(String[] args) {
PrintWriter out = null; // to print out the result
try {
out = new PrintWriter(
new BufferedWriter(
new FileWriter("C:\\Factorials.txt")));
} catch (IOException e) {
e.printStackTrace();
System.exit(0);
}
int numToFactorial = 1000000; // one million
// first, compute 1000!, 2000!/1000!, 3000!/2000!...
// and put into a BigInteger[]
BigInteger[] products = new BigInteger[1000]; // 1000 = sqrt(1000000) (arbitrary choice)
for (int i = 0, n = 1 ; i < products.length ; i++) { // n denotes the next number to multiply by to get a factorial
products[i] = new BigInteger(n + "");
for (int j = 0 ; j < (numToFactorial / products.length) ; j++, n++) {
products[i] = products[i].multiply(new BigInteger(n + ""));
}
}
// reduce products to a smaller array (arbitrary size - intended for quicker computation)
BigInteger[] products2 = new BigInteger[4];
for (int i = 0, p = 0 ; i < products2.length ; i++) { // p denotes index of products[]
products2[i] = BigInteger.ONE; // start off with one - makes the next for loop neater
int x = products.length / products2.length; // so we don't have to calculate it every time
// in the next for-loop (to speed things up)
for (int j = 0 ; j < x ; j++, p++) {
products2[i] = products2[i].multiply(products[p]);
}
}
// for the final answer
BigInteger product = BigInteger.ONE;
for (int i = 0 ; i < products2.length ; i++) { // this loop will take LOTS of time
product = product.multiply(products2[i]);
}
out.print(numToFactorial + "! = " + product);
out.close();
}
}
```

I'm uploading a text file containing the number at the moment. My computer ain't liking it

Bad speling makes me [sic]

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**kylekatarn****Member**- Registered: 2005-07-24
- Posts: 445

You took so many hours because you used Java:(

I also use Java and it's very cool because all the OO' stuff but when it comes to low optimizations+memory+speed I always try a C/C++ approach first.

ps: Mathematica took 0.02 sec to find (10^6)! ..dont ask me how

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