a(n) = (1/8)*A357285.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =1a(8) =4a(9) =13a(10) =38a(11) =99a(12) =240a(13) =565a(14) =1274a(15) =2799a(16) =6052a(17) =12857a(18) =26958a(19) =56099a(20) =115704a(21) =237133a(22) =484002a(23) =983543a(24) =1992012a(25) =4026017a(26) =8118262a(27) =16342347a(28) =32860832a(29) =65998837