Question 166155
Look at the difference between terms,
1,3=2
3,6=3
6,10=4
10,15=5
15,21=6
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First term=1
Second term=First term +2=1+2
Third term=Second term+3=1+2+3
Fourth term=Third term+4=1+2+3+4
Starting to see a pattern here...
Nth term=(N-1)term+N=1+2+3+...+(N-1)+N
Look like the terms follow,
{{{T[N]=sum( i, i=1, N )}}}
{{{T[25]=sum( i, i=1, 25 )=325}}}