a(n) = 3^n + 6^n + 7^n.

Terms

a(0) =3a(1) =16a(2) =94a(3) =586a(4) =3778a(5) =24826a(6) =165034a(7) =1105666a(8) =7450978a(9) =50450986a(10) =343000474a(11) =2340300946a(12) =16018600978a(13) =109951298746a(14) =756592019914