a(n) = Sum_{k|n} binomial(n-1,k-1).

Terms

a(0) =1a(1) =2a(2) =2a(3) =5a(4) =2a(5) =17a(6) =2a(7) =44a(8) =30a(9) =137a(10) =2a(11) =695a(12) =2a(13) =1731a(14) =1094a(15) =6907a(16) =2a(17) =30653a(18) =2a(19) =97244a(20) =38952a(21) =352739a(22) =2a(23) =1632933a(24) =10628a(25) =5200327a(26) =1562602a(27) =20357264a(28) =2a(29) =87716708