a(n) = binomial((n+1)*2^n, n)/(n+1).A177410a(n) = binomial((n+1)*2^n, n)/(n+1).Terms a(0) =1a(1) =2a(2) =22a(3) =1240a(4) =316316a(5) =343855008External referencesoeis: A177410