a(n) = Sum_{d|n} mu(n/d) * binomial(n+d-2, n-1).

Terms

a(0) =1a(1) =1a(2) =5a(3) =16a(4) =69a(5) =226a(6) =923a(7) =3312a(8) =12825a(9) =47896a(10) =184755a(11) =700712a(12) =2704155a(13) =10373455a(14) =40113421a(15) =154946976a(16) =601080389a(17) =2332498482a(18) =9075135299a(19) =35338355380a(20) =137846298360a(21) =538213522254