[1] However, unlike the triangular and square numbers, the patterns involved in the construction of nonagonal numbers are not rotationally symmetrical.
Specifically, the nth nonagonal number counts the dots in a pattern of n nested nonagons, all sharing a common corner, where the ith nonagon in the pattern has sides made of i dots spaced one unit apart from each other.
denote the nth nonagonal number, and using the formula
for the nth triangular number, If x is an integer, then n is the x-th nonagonal number.
This article about a number is a stub.