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

Terms

a(0) =10a(1) =76a(2) =538a(3) =3772a(4) =26410a(5) =184876a(6) =1294138a(7) =9058972a(8) =63412810a(9) =443889676a(10) =3107227738a(11) =21750594172a(12) =152254159210