a(n) = 3^n + 7^n + 8^n.

Terms

a(0) =3a(1) =18a(2) =122a(3) =882a(4) =6578a(5) =49818a(6) =380522a(7) =2922882a(8) =22548578a(9) =174591018a(10) =1356276122a(11) =10567438482a(12) =82561295378a(13) =646646418618