a(n) = 10^n + 11^n.

Terms

a(0) =2a(1) =21a(2) =221a(3) =2331a(4) =24641a(5) =261051a(6) =2771561a(7) =29487171a(8) =314358881a(9) =3357947691a(10) =35937424601a(11) =385311670611