a(n) = 6*a(n-1) - 9*a(n-2) + n + 1.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =9a(5) =43a(6) =185a(7) =732a(8) =2737a(9) =9845a(10) =34449a(11) =118102a(12) =398585a(13) =1328607a(14) =4384393a(15) =14348912a(16) =46633953a(17) =150663529a(18) =484275617a(19) =1549681962a(20) =4939611241a(21) =15690529811a(22) =49686677721a(23) =156905298052a(24) =494251688849