

Subject:
factorials for addition?
Category: Science > Math Asked by: lawboyga List Price: $2.00 
Posted:
17 Mar 2006 11:32 PST
Expires: 16 Apr 2006 12:32 PDT Question ID: 708478 
I know what a factorial is, but I can't remember whether there is a word and/or formula taking a number, lets say 5, and adding 5+4+3+2+1, which is 15. Does this function (that's probably not the right word, I'm not a mathematition, have a word, like "factorial"? If so, what is it? 

There is no answer at this time. 

Subject:
answer
From: lopharga on 17 Mar 2006 13:00 PST 
There is no special name for this function. But there is a simple formula: 1 + 2 + 3 + ... + n = n(n+1)/2 The proof can be found here: http://mathworld.wolfram.com/ArithmeticSeries.html These numbers are sometimes called triangular: http://mathworld.wolfram.com/TriangularNumber.html 
Subject:
Re: factorials for addition?
From: lawboyga on 17 Mar 2006 16:27 PST 
Thanks lopharga. Quick aside question. It seems like many of the easier questions on GA are answered for free, in the comments. What's your incentive? ARe you trying to become a Researcher, or just a nice guy who stumbled upon my question? Or is there another explanation. Thanks again. 
Subject:
Re: factorials for addition?
From: ansel001ga on 17 Mar 2006 19:00 PST 
The motivation varies from person to person. Some people hope to become one of the official paid researchers, some just like to help, and some like to show how smart they are. 
Subject:
Re: factorials for addition?
From: lopharga on 18 Mar 2006 16:21 PST 
I answer questions just for fun when i have nothing else to do, and i need no money for this. 
Subject:
Re: factorials for addition?
From: lawboyga on 23 Mar 2006 11:18 PST 
OK. Thanks to both of you. 
Subject:
Re: factorials for addition?
From: myoaringa on 10 Apr 2006 03:53 PDT 
Amitrangraga, Your comment will probably be deleteed because you posted an email address. That's nono here. Lawboy, Here is a definition of factorial: "In mathematics, the factorial of a natural number n is the product of the positive integers less than or equal to n. This is written as n! and pronounced "n factorial". The notation n! was introduced by Christian Kramp in 1808." en.wikipedia.org/wiki/Factorial And here is another with an example: "The product of a series of consecutive positive integers from 1 to a given number (n). It is expressed with the symbol ( ! ). For example, 5! = 5x4x3x2x1 = 120. As a rule (n!+n) is evenly divisible by n." dorakmt.tripod.com/mtd/glosmath.html 
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