Wednesday

April 16, 2014

April 16, 2014

Posted by **John** on Saturday, October 2, 2010 at 7:23pm.

I keep seeing n!= n(n+1)/2 but that's not working.

For example: 5!= 120 but 5(6)/2 or 6(5/2) is 15; a far cry from 120. I don't understand what I'm doing wrong; distributing gives (n^2+n)/2 which is incorrect.

Also the example I saw as the supposed true story used 1-100 and showed it as 101(100/2) = 5050.

What am I missing here?

- math (Gaussian n! formula) -
**bobpursley**, Saturday, October 2, 2010 at 7:35pmI dont know where you got that formula, it is obviously wrong.

2!=2*1 which does not equal 2*3/2

- math (Gaussian n! formula) -
**MathMate**, Saturday, October 2, 2010 at 7:38pmThere must be a confusion somewhere.

Gauss as a small boy in school was told by his teacher to add numbers from 1 to 100, after which he can play outside. While everyone else was still adding away, he went out and played after about 2 minutes. His teacher was about to punish him when he told the teacher he finished!

When asked how he did it, he answered:

Write the numbers 1-100 and 100-1 one on top of the other and add vertically. We have 100 sums of 101 for two rows, so the sum for one row is 101*100/2=5050.

So probably this 1-100 = 5050 formula became the famous Gauss formula, but not for factorial.

If you are looking for an*approximation*to the factorial function, i.e. f(n)=n! (approximately), use the Stirling formula.

lim n->∞ n!=√(2πn)(n/e)^{n}.

See:

http://en.wikipedia.org/wiki/Stirling%27s_approximation

**Related Questions**

Math - How would I determine if a set of numbers if Gaussian or non Gaussian?

physics2 - A Gaussian surface encloses two charges. The total electric flux ...

gaussian elimination - 4. Solve the following linear system using Gaussian ...

Chemistry - the formula H2O2 is an example of 1.molecular formula 2. an ...

algebra - What is the slope of a line through (-5,2) and (6,7) in the standard(x...

7th grade math - I hope this makes sense, but my teacher said he wants all ...

distance formula - Hey thanks, stupid negative..... Ok now I'm trying to figure ...

math - how do you solve by gaussian elimation 2x+y=3 3x-2y=1

factorial help!!! - i just need help with factorials I assume you know what a ...

math - Okay. so say their is a list of numbers: x y 0 3 1 5 2 7 3 9 4 11 I know ...