Expansion of g.f. 1/((1-x)*(1-2*x)*(1-6*x)).

Terms

a(0) =1a(1) =9a(2) =61a(3) =381a(4) =2317a(5) =13965a(6) =83917a(7) =503757a(8) =3023053a(9) =18139341a(10) =108838093a(11) =653032653a(12) =3918204109a(13) =23509241037a(14) =141055478989a(15) =846332939469