a(1) = a(2) = 1; a(n) = Sum_{1 < k < n, k not dividing n} a(k).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =3a(5) =4a(6) =10a(7) =18a(8) =37a(9) =71a(10) =146a(11) =285a(12) =577a(13) =1143a(14) =2293a(15) =4570a(16) =9160a(17) =18277a(18) =36597a(19) =73118a(20) =146301a(21) =292466a(22) =585079a(23) =1169848a(24) =2340003a(25) =4679431a(26) =9359402a(27) =18717687a(28) =37436529a(29) =74870685