A001333(n), n >= 1, convolved twice with itself.

Terms

a(0) =1a(1) =9a(2) =48a(3) =204a(4) =765a(5) =2649a(6) =8680a(7) =27312a(8) =83313a(9) =247985a(10) =723624a(11) =2077164a(12) =5880797a(13) =16454865a(14) =45577200a(15) =125130432a(16) =340882113a(17) =922265721a(18) =2479938368a(19) =6631802220a(20) =17646603933a(21) =46744464745a(22) =123314065944a(23) =324085913136a(24) =848801213425