481174domain: NAppears in sequencesa(3) = 2, a(4) = 3; for n > 4, a(n) = {a(n-2)}+{a(n-1)}, where {a} means largest prime <= a.at n=27A065435Number of n X n binary arrays symmetric under 90 degree rotation with all ones connected only in a 0111-1100-0111 pattern in any orientation.at n=18A147374