243392domain: NAppears in sequencesn*a(n) = 2*(2*n-1)*a(n-1) + 4*(n-1)*a(n-2) with a(0) = 1.at n=9A006139Duplicate of A006139.at n=9A084607Square array of expansions of 1/sqrt(1-4x-4*k*x^2), read by antidiagonals.at n=56A110135Triangle of Delannoy paths counted by number of diagonal steps not preceded by an east step.at n=45A110446