a(n) = floor(3^n/n^2).

Terms

a(0) =3a(1) =2a(2) =3a(3) =5a(4) =9a(5) =20a(6) =44a(7) =102a(8) =243a(9) =590a(10) =1464a(11) =3690a(12) =9433a(13) =24402a(14) =63772a(15) =168151a(16) =446851a(17) =1195742a(18) =3219560a(19) =8716961a(20) =23719621a(21) =64836900a(22) =177964421a(23) =490329056a(24) =1355661775a(25) =3760156550a(26) =10460353203a(27) =29179582212a(28) =81605680576a(29) =228767924549