a(n) = binomial(2^n + n + 1, n).A132684a(n) = binomial(2^n + n + 1, n).Terms a(0) =1a(1) =4a(2) =21a(3) =220a(4) =5985a(5) =501942a(6) =143218999a(7) =145944307080External referencesoeis: A132684