6thtriangularnumber

<-- Enter triangular number statement
  

Calculate triangular number 6

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

Given n = 6, we have:
T6  =  6(6 + 1)
  2

T6  =  6(7)
  2

T6  =  42
  2

T6 = 21