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

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =2a(7) =5a(8) =14a(9) =45a(10) =165a(11) =667a(12) =2944a(13) =14076a(14) =72492a(15) =400021a(16) =2354550a(17) =14725238a(18) =97508022a(19) =681552736a(20) =5014584788a(21) =38740015634a(22) =313536416650