a(1)=1, a(n) = n*3^(n-1) + a(n-1).

Terms

a(0) =1a(1) =7a(2) =34a(3) =142a(4) =547a(5) =2005a(6) =7108a(7) =24604a(8) =83653a(9) =280483a(10) =930022a(11) =3055786a(12) =9964519a(13) =32285041a(14) =104029576a(15) =333612088a(16) =1065406345a(17) =3389929279a(18) =10750918570a(19) =33996147910a(20) =107218620331a(21) =337346390797