a(n) = 2^n + 5^n + 8^n.

Terms

a(0) =3a(1) =15a(2) =93a(3) =645a(4) =4737a(5) =35925a(6) =277833a(7) =2175405a(8) =17168097a(9) =136171365a(10) =1083508473a(11) =8638764765a(12) =68963621457a(13) =550976525205