a(n) = floor(n!*exp(-n)).

Terms

a(0) =1a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =1a(7) =4a(8) =13a(9) =44a(10) =164a(11) =666a(12) =2943a(13) =14075a(14) =72491a(15) =400020a(16) =2354549a(17) =14725237a(18) =97508021a(19) =681552735a(20) =5014584787a(21) =38740015633a(22) =313536416649