a(n) = 384*4^n - 576*3^n + 220*2^n - 14.

Terms

a(0) =14a(1) =234a(2) =1826a(3) =10770a(4) =55154a(5) =260274a(6) =1167026a(7) =5059890a(8) =21442994a(9) =89438514a(10) =368866226a(11) =1509026610a(12) =6137242034a(13) =24853275954a(14) =100327829426a(15) =404059098930