3rdpentagonalnumber

<-- Enter pentagonal number statement
  

Calculate pentagonal number 3

The formula for pentagonal number n is as follows
Pn  =  n(3n - 1)
  2

Given n = 3, we have:
P3  =  3(3(3) - 1)
  2

P3  =  3(9 - 1)
  2

P3  =  3(8)
  2

P3  =  24
  2

P3 = 12