Nonagonal number
= Nonagonal number
{wiki=Nonagonal_number}
A nonagonal number is a figurate number that represents a nonagon, which is a polygon with nine sides. Nonagonal numbers can be calculated using the formula: \\\[ N_n = \\frac\{n(7n - 5)\}\{2\} \\\] where \\( N_n \\) is the \\( n \\)-th nonagonal number and \\( n \\) is a positive integer representing the position in the sequence of nonagonal numbers.