a(n) = (4^n+8*(-5)^n)/9.

Terms

a(0) =1a(1) =-4a(2) =24a(3) =-104a(4) =584a(5) =-2664a(6) =14344a(7) =-67624a(8) =354504a(9) =-1706984a(10) =8797064a(11) =-42936744a(12) =218878024a(13) =-1077612904a(14) =5455173384a(15) =-27007431464a(16) =136110899144a(17) =-676259528424