a(n) = 2^n + 8^n.

Terms

a(0) =2a(1) =10a(2) =68a(3) =520a(4) =4112a(5) =32800a(6) =262208a(7) =2097280a(8) =16777472a(9) =134218240a(10) =1073742848a(11) =8589936640a(12) =68719480832a(13) =549755822080