5thpentagonalnumber

<-- Enter pentagonal number statement
  

Calculate pentagonal number 5

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

Given n = 5, we have:
P5  =  5(3(5) - 1)
  2

P5  =  5(15 - 1)
  2

P5  =  5(14)
  2

P5  =  70
  2

P5 = 35