99857989632domain: NAppears in sequencesNumber of n X 2 0..2 arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling two exactly once.at n=15A268898a(1)= 2. For n > 1, a(n) is the least number k such that k, k - a(n-1) and k + a(n-1) all have n prime divisors counted by multiplicity.at n=31A365852