A029913 Start with n; if prime, stop; repeatedly sum squares of prime factors (counted with multiplicity), until reach 16 or a prime; set a(n) = 0 if no limit exists.

2, 3, 17, 5, 13, 7, 17, 59, 29, 11, 17, 13, 53, 293, 16, 17, 16, 19, 16, 16, 16, 23, 16, 16, 16, 16, 16, 29, 16, 31, 16, 16, 16, 16, 16, 37, 16, 16, 16, 41, 16, 43, 16, 16, 16, 47, 16, 16, 16, 16, 16, 53, 16, 16, 16, 16, 16, 59, 16, 61, 16, 16, 16, 16, 16, 67, 16, 16, 16, 71