a(n) = Sum_{d|n and gcd(d, n/d)=1} binomial(n,d).

Terms

a(0) =1a(1) =3a(2) =4a(3) =5a(4) =6a(5) =42a(6) =8a(7) =9a(8) =10a(9) =308a(10) =12a(11) =728a(12) =14a(13) =3538a(14) =3474a(15) =17a(16) =18a(17) =48792a(18) =20a(19) =20370a(20) =117632a(21) =705686a(22) =24a(23) =737520a(24) =26a(25) =10400952a(26) =28a(27) =1204544a(28) =30a(29) =185903342