a(n) = binomial(n,12).

Terms

a(0) =1a(1) =13a(2) =91a(3) =455a(4) =1820a(5) =6188a(6) =18564a(7) =50388a(8) =125970a(9) =293930a(10) =646646a(11) =1352078a(12) =2704156a(13) =5200300a(14) =9657700a(15) =17383860a(16) =30421755a(17) =51895935a(18) =86493225a(19) =141120525a(20) =225792840a(21) =354817320a(22) =548354040a(23) =834451800a(24) =1251677700a(25) =1852482996a(26) =2707475148a(27) =3910797436a(28) =5586853480