a(n) = T(2n+1, n+2), T given by A027948.

Terms

a(0) =1a(1) =5a(2) =41a(3) =189a(4) =674a(5) =2098a(6) =6050a(7) =16703a(8) =44995a(9) =119575a(10) =315460a(11) =829060a(12) =2174596a(13) =5698329a(14) =14924829a(15) =39081553a(16) =102326310a(17) =267905078a(18) =701397990a(19) =1836299475a(20) =4807512695a(21) =12586252715a(22) =32951261576a(23) =86267550344a(24) =225851410184a(25) =591286703533