5thtriangularnumber

<-- Enter triangular number statement
  

Calculate triangular number 5

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

Given n = 5, we have:
T5  =  5(5 + 1)
  2

T5  =  5(6)
  2

T5  =  30
  2

T5 = 15