a(n) = 4^n + 6^n + 8^n.

Terms

a(0) =3a(1) =18a(2) =116a(3) =792a(4) =5648a(5) =41568a(6) =312896a(7) =2393472a(8) =18522368a(9) =144557568a(10) =1135256576a(11) =8956925952a(12) =70913036288a(13) =562883616768