a(n) = 1^n + 6^n + 7^n.

Terms

a(0) =3a(1) =14a(2) =86a(3) =560a(4) =3698a(5) =24584a(6) =164306a(7) =1103480a(8) =7444418a(9) =50431304a(10) =342941426a(11) =2340123800a(12) =16018069538a(13) =109949704424a(14) =756587236946