4thpentagonalnumber

<-- Enter pentagonal number statement
  

Calculate pentagonal number 4

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

Given n = 4, we have:
P4  =  4(3(4) - 1)
  2

P4  =  4(12 - 1)
  2

P4  =  4(11)
  2

P4  =  44
  2

P4 = 22