a(n) = (n+1)*binomial(n+1, 15).

Terms

a(0) =15a(1) =256a(2) =2312a(3) =14688a(4) =73644a(5) =310080a(6) =1139544a(7) =3751968a(8) =11277222a(9) =31380096a(10) =81719000a(11) =200880160a(12) =469364220a(13) =1048380480a(14) =2249204040a(15) =4653525600a(16) =9316746045a(17) =18103127040a(18) =34226224560a(19) =63102895680a(20) =113678010600a(21) =200444492160a(22) =346475391120a(23) =587908889280