- triangle-number? nprocedure
- square-number? nprocedure
- pentagonal-number? nprocedure
- hexagonal-number? nprocedure
- heptagonal-number? nprocedure
- octagonal-number? nprocedure
- n
- integer
These functions check whether the input is a polygonal number of the types triangle, square, pentagonal, hexagonal, heptagonal and octogonal respectively.
Wikipedia: Polygonal Number