G.f.: A(x) = exp( Sum_{n>=1} 3^n * x^n/(n*(1+x^n)) ).

Terms

a(0) =1a(1) =3a(2) =6a(3) =21a(4) =60a(5) =174a(6) =537a(7) =1596a(8) =4776a(9) =14358a(10) =43053a(11) =129126a(12) =387438a(13) =1162272a(14) =3486678a(15) =10460307a(16) =31380756a(17) =94141830a(18) =282426288a(19) =847278282a(20) =2541833808a(21) =7625503749a(22) =22876509444a(23) =68629525032a(24) =205888582014a(25) =617665741140