a(n) = 2*11^n+1.

Terms

a(0) =3a(1) =23a(2) =243a(3) =2663a(4) =29283a(5) =322103a(6) =3543123a(7) =38974343a(8) =428717763a(9) =4715895383a(10) =51874849203a(11) =570623341223