a(1)=1, a(n) = n*7^(n-1) + a(n-1).

Terms

a(0) =1a(1) =15a(2) =162a(3) =1534a(4) =13539a(5) =114381a(6) =937924a(7) =7526268a(8) =59409477a(9) =462945547a(10) =3570173286a(11) =27298094202a(12) =207234827815