a(n) = 11^n - 3^n + 1.

Terms

a(0) =1a(1) =9a(2) =113a(3) =1305a(4) =14561a(5) =160809a(6) =1770833a(7) =19484985a(8) =214352321a(9) =2357928009a(10) =25937365553a(11) =285311493465