a(n) = A000041(A000009(n)).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =2a(5) =3a(6) =5a(7) =7a(8) =11a(9) =22a(10) =42a(11) =77a(12) =176a(13) =385a(14) =1002a(15) =3010a(16) =8349a(17) =26015a(18) =105558a(19) =386155a(20) =1741630a(21) =9289091a(22) =49995925a(23) =304801365a(24) =2291320912a(25) =18440293320a(26) =172389800255