a(n+1) = 5*a(n) - n.

Terms

a(0) =1a(1) =4a(2) =18a(3) =87a(4) =431a(5) =2150a(6) =10744a(7) =53713a(8) =268557a(9) =1342776a(10) =6713870a(11) =33569339a(12) =167846683a(13) =839233402a(14) =4196166996a(15) =20980834965a(16) =104904174809a(17) =524520874028