Second column of triangle A055584.

Terms

a(0) =1a(1) =6a(2) =25a(3) =88a(4) =280a(5) =832a(6) =2352a(7) =6400a(8) =16896a(9) =43520a(10) =109824a(11) =272384a(12) =665600a(13) =1605632a(14) =3829760a(15) =9043968a(16) =21168128a(17) =49152000a(18) =113311744a(19) =259522560a(20) =590872576a(21) =1337982976a(22) =3014656000a(23) =6761218048a(24) =15099494400a(25) =33587986432a(26) =74440507392a(27) =164416716800a(28) =361985212416a(29) =794568949760