The numbers generated by es(ex-1) where s is an integer are discussed by many for s = 1. The general case also is discussed by Touchard, Riordan and others.

Let f be a positive definite binary quadratic form with rational coefficients. We shall call a point (x, y) in E2 with integers x and y a Pythagorean point of f when f(x, y) = z2 is satisfied with some integer z, and shall prove the following theorem.

A ring R (associative ring) is said to be fully ordered provided that R is a linearly ordered set under a relation such that for any a, b and c in R, implies that and if c ε 0 then and . We say a subset K of R is convex provided that if a, b ε K such that then the interval [a, b] is a subset of K. Obviously an additive subgroup K of R is convex if and only if b ε K and b > 0 implies [a, b] ⊆ K.