Start with k=2*n, and until k+1 is prime, apply the map k -> k*(least prime factor of (k+1)); then a(n) = k+1, or 0 if k+1 never reaches a prime.

A288212

Start with k=2*n, and until k+1 is prime, apply the map k -> k*(least prime factor of (k+1)); then a(n) = k+1, or 0 if k+1 never reaches a prime.