a(0) = 0; a(n) = 7*a(n-1) + 7.

Terms

a(0) =0a(1) =7a(2) =56a(3) =399a(4) =2800a(5) =19607a(6) =137256a(7) =960799a(8) =6725600a(9) =47079207a(10) =329554456a(11) =2306881199a(12) =16148168400a(13) =113037178807a(14) =791260251656