Question

A set S of ordered pairs of integers is defined recursively by
(1) (1, 1) are elements of S
(2) if (m, n) are elements of S, then (m + 2, n) are elements of S, and (m, n + 2) are elements of S, and (m + 1, n + 1) are elements of S.
There is a simple description of the ordered pairs in S. What is it?