Pentagonal number
= Pentagonal number
{wiki=Pentagonal_number}
A pentagonal number is a figurate number that represents a pentagon. The \\( n \\)-th pentagonal number can be calculated using the formula: \\\[ P(n) = \\frac\{n(3n - 1)\}\{2\} \\\] where \\( n \\) is a positive integer. The sequence of pentagonal numbers begins with 1, 5, 12, 22, 35, and so on.