a(n) = (9^n - (-7)^n)/(9 - (-7)).

Terms

a(0) =1a(1) =2a(2) =67a(3) =260a(4) =4741a(5) =25862a(6) =350407a(7) =2330120a(8) =26735881a(9) =200269322a(10) =2084899147a(11) =16786765580a(12) =164922177421