a(n) = self-convolution of row n of array T given by A027052.

Terms

a(0) =1a(1) =2a(2) =3a(3) =12a(4) =53a(5) =222a(6) =899a(7) =3540a(8) =13657a(9) =51882a(10) =194727a(11) =723760a(12) =2668453a(13) =9771870a(14) =35577935a(15) =128887616a(16) =464885073a(17) =1670362418a(18) =5981289455a(19) =21352860808a(20) =76020123293a(21) =269977176422a(22) =956644165503