RE: [Math4u] formula

These are called the the triangular numbers.

 

1: 0

2: 0 0

3: 0 0 0

4: 0 0 0 0

etc.

 

Sequence:

S(n) = 1 + 2 + ... + (n-1) + n

 

Reverse the order:

S(n) = n + (n-1) + ... + 2 + 1

 

Add:

 

2S(n) = (n+1) + (n+1) + ... + (n+1) + (n+1)

2S(n) = n(n+1)

S(n) = n(n+1)/2

 

 

 

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From: Math4u@yahoogroups.com [mailto:Math4u@yahoogroups.com] On Behalf Of adilelfahmi
Sent: 02 December 2007 02:04
To: Math4u@yahoogroups.com
Subject: [Math4u] formula

hey anyone knows formula for this:
1 to 2 equal 3
1 to 5 equal 15(1+2+3+4+5)
etc.
anyone have it?
sorry if my english is bad, i'm indonesian

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