a(n) = Sum_{d|n} (d!)^(n/d-1).

Terms

a(0) =1a(1) =2a(2) =2a(3) =4a(4) =2a(5) =12a(6) =2a(7) =34a(8) =38a(9) =138a(10) =2a(11) =1546a(12) =2a(13) =5106a(14) =15698a(15) =54274a(16) =2a(17) =889314a(18) =2a(19) =5689090a(20) =25448258a(21) =39917826a(22) =2a(23) =2486196610a(24) =207360002a(25) =6227024898a(26) =131683574018a(27) =215393466370a(28) =2a(30) =2