Definition:Second Pentagonal Number

Definition
The second pentagonal numbers are those denumerating a collection of objects which can be arranged in the form of a regular pentagon.

They can be denoted:
 * $P_1, P_2, P_3, \ldots$

Also see

 * Equivalence of Definitions of Second Pentagonal Number


 * Definition:Pentagonal Number
 * Definition:Generalized Pentagonal Number