a(n) = (A051894(n) - 1)/2.

Terms

a(0) =0a(1) =1a(2) =4a(3) =9a(4) =21a(5) =40a(6) =79a(7) =138a(8) =250a(9) =415a(10) =707a(11) =1126a(12) =1836a(13) =2837a(14) =4466a(15) =6723a(16) =10290a(17) =15167a(18) =22672a(19) =32805a(20) =48071a(21) =68470a(22) =98610a(23) =138491a(24) =196474a(25) =272559a(26) =381540a(27) =523417a(28) =724042a(29) =983415