Decagonal number
= Decagonal number
{wiki=Decagonal_number}
A decagonal number is a figurate number that represents a decagon, which is a ten-sided polygon. The \\(n\\)-th decagonal number can be calculated using the formula: \\\[ D_n = \\frac\{n(4n - 3)\}\{2\} \\\] where \\(D_n\\) is the \\(n\\)-th decagonal number and \\(n\\) is a positive integer.