Number of n-step mappings with 4 inputs.

Terms

a(0) =0a(1) =1a(2) =15a(3) =60a(4) =154a(5) =315a(6) =561a(7) =910a(8) =1380a(9) =1989a(10) =2755a(11) =3696a(12) =4830a(13) =6175a(14) =7749a(15) =9570a(16) =11656a(17) =14025a(18) =16695a(19) =19684a(20) =23010a(21) =26691a(22) =30745a(23) =35190a(24) =40044a(25) =45325a(26) =51051a(27) =57240a(28) =63910a(29) =71079