a(n) = Sum_{d|n} Sum{t|d} (n/d)*moebius(d/t)*binomial(3*t,t)/(3*d^2).

A244036

a(n) = Sum_{d|n} Sum{t|d} (n/d)*moebius(d/t)*binomial(3*t,t)/(3*d^2).

Terms

    a(0) =1a(1) =3a(2) =6a(3) =16a(4) =45a(5) =186a(6) =798a(7) =3860a(8) =19305a(9) =100235a(10) =533170a(11) =2897760a(12) =16020576a(13) =89899754a(14) =510914850a(15) =2936007952a(16) =17036988583a(17) =99718499907a(18) =588166176678

External references