a(2*n) = A001570(n), a(2*n+1) = A011943(n+1).

Terms

a(0) =1a(1) =7a(2) =13a(3) =97a(4) =181a(5) =1351a(6) =2521a(7) =18817a(8) =35113a(9) =262087a(10) =489061a(11) =3650401a(12) =6811741a(13) =50843527a(14) =94875313a(15) =708158977a(16) =1321442641a(17) =9863382151a(18) =18405321661a(19) =137379191137a(20) =256353060613