45501743domain: NAppears in sequencesa(n) = T(n, n-2), T given by A026552. Also a(n) = number of integer strings s(0), ..., s(n) counted by T, such that s(n) = 2.at n=20A026555a(n) = Sum_{k=0..2n-2} T(n,k) * T(n,k+2), with T given by A026519.at n=9A027264a(n) = Sum_{k=0..2n-2} T(n,k) * T(n,k+2), with T given by A026552.at n=9A027274