a(n) = 4*a(n-1) + a(n-2) - a(n-3) - a(n-5).

Terms

a(0) =5a(1) =21a(2) =88a(3) =368a(4) =1538a(5) =6427a(6) =26857a(7) =112229a(8) =468978a(9) =1959746a(10) =8189306a(11) =34221135a(12) =143001871a(13) =597570335a(14) =2497102330a(15) =10434788478a(16) =43604464772a(17) =182212543365a(18) =761422279419