a(n) = 7*11^n-1.

Terms

a(0) =6a(1) =76a(2) =846a(3) =9316a(4) =102486a(5) =1127356a(6) =12400926a(7) =136410196a(8) =1500512166a(9) =16505633836a(10) =181561972206