For n>0, a(n) = least positive number m such that 4^m == +1 or -1 (mod 2n + 1), with a(0) = 0 by convention.

A003569

For n>0, a(n) = least positive number m such that 4^m == +1 or -1 (mod 2n + 1), with a(0) = 0 by convention.