Polygonal number
= Polygonal number
{title2=$P_{s,n}$}
For <integers> $s\ge3$ and $n\ge1$, the $n$th $s$-gonal number is $P_{s,n}=((s-2)n^2-(s-4)n)/2$. Its successive differences form an <arithmetic progression>. The cases $s=3,4,5,6$ give <triangular numbers>, <square numbers>, <pentagonal numbers>, and <hexagonal numbers>.