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Finding a formula for a difficult sequence

  • #1

Homework Statement

I'm trying to find a formula for 1, 3, 6, 10 ... for n=2,3,4,....







The Attempt at a Solution


Well I know that the difference between each number is increasing by 1. For example, the difference between 1 and 3 is 2, between 3 and 6 is 3, between 6 and 10 is 4 and so on. But, I just don't see a formula.
 

Answers and Replies

  • #2
256
0
Hi! [tex]a_n = \sum_{ k = 1 }^n k = \frac{ n ( n + 1 ) }{ 2 }[/tex]
 
  • #3
For some reason, I can't read that.
 

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