a(n) = least positive integer solution k to h(k) = h(k-1)+h(k-2)+...+h(k-n), where h(n) is the length of n, f(n), f(f(n)), ...., 1 in the Collatz (or 3x + 1) problem. (The earliest "1" is meant.)

1. Recall that f(n) = n/2 if n is even; = 3n + 1 if n is odd. 2. Problem: Is a(n) defined for all n, that is, does a positive integer solution k to h(n) = h(k-1)+h(k-2)+...+h(k-n) always exist?