a(n) is the number of divisors of A000178(n).

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =18a(5) =72a(6) =234a(7) =1088a(8) =3600a(9) =10416a(10) =28080a(11) =124080a(12) =387828a(13) =1921024a(14) =6926400a(15) =20941344a(16) =54934880a(17) =251328000a(18) =810152280a(19) =4254092800a(20) =15266200950a(21) =46208448000a(22) =129674387920a(23) =640501862400