51981domain: NAppears in sequencesa(n) = Sum_{k=0..n} (k+1) * A026780(n, k).at n=11A027251Surround numbers of an n X 2 rectangle when n is odd.at n=11A061525Twin prime products minus 2.at n=15A124659Numbers k such that phi(k, 2) = phi(k+1, 2), where phi(k, 2) = A002472(k).at n=16A301868