pub fn figurate(s: i64, n: i64) -> i64
Return the nth figurate number with s sides
Panics if s is less than three
use reikna::figurate::figurate;
let a = figurate(3, 3);
let b = figurate(45, 91);
let c = figurate(17, 5);
assert_eq!(vec![a, b, c], vec![6, 176176, 155]);