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

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =3a(5) =5a(6) =12a(7) =27a(8) =89a(9) =296a(10) =1426a(11) =7108a(12) =58499a(13) =483330a(14) =6711480a(15) =109420549a(16) =2973772212a(17) =98872765938