(A331763(n) - A331755(n+1))/2.

Terms

a(0) =4a(1) =12a(2) =32a(3) =69a(4) =121a(5) =191a(6) =304a(7) =432a(8) =582a(9) =799a(10) =1042a(11) =1320a(12) =1661a(13) =2043a(14) =2457a(15) =3023a(16) =3575a(17) =4195a(18) =4920a(19) =5693a(20) =6465a(21) =7487a(22) =8502a(23) =9617a(24) =10833a(25) =12173a(26) =13526a(27) =15146a(28) =16693a(29) =18397