31212003420domain: NAppears in sequencesa(n) = binomial(2*n-1, n) - binomial(2*n-1, n+3).at n=19A026016Expansion of (1+x^2*C^4)*C, where C = (1 - sqrt(1-4*x))/(2*x) is g.f. for Catalan numbers, A000108.at n=20A071725