70191domain: NAppears in sequencesa(n) = Sum_{k<=n} A007955(k) * A000027(n-k+1) = Sum_{k<=n} A007955(k) * (n-k+1), where A007955(m) = product of divisors of m.at n=20A174934Number of n X 4 0..1 arrays avoiding 0 0 0 and 0 1 1 horizontally and 0 0 1 and 1 0 1 vertically.at n=21A207020