Let f map (x, y) to (x+y, x*y). Start from (X, X) and iterate f n times. Then a(n) is the coefficient of X^n in the polynomial in X that expresses the x-coordinate of the obtained position.

A343952

Let f map (x, y) to (x+y, x*y). Start from (X, X) and iterate f n times. Then a(n) is the coefficient of X^n in the polynomial in X that expresses the x-coordinate of the obtained position.