7thtriangularnumber

<-- Enter triangular number statement
  

Calculate triangular number 7

The formula for triangular number n is as follows
Tn  =  n(n + 1)
  2

Given n = 7, we have:
T7  =  7(7 + 1)
  2

T7  =  7(8)
  2

T7  =  56
  2

T7 = 28