a(n) = 3^n + 10^n.

Terms

a(0) =2a(1) =13a(2) =109a(3) =1027a(4) =10081a(5) =100243a(6) =1000729a(7) =10002187a(8) =100006561a(9) =1000019683a(10) =10000059049a(11) =100000177147