a(n) = 2*a(n-1) + 4*a(n-2) - 6*a(n-3) - 3*a(n-4).

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =2a(5) =8a(6) =18a(7) =53a(8) =124a(9) =328a(10) =780a(11) =1969a(12) =4718a(13) =11648a(14) =28014a(15) =68405a(16) =164824a(17) =400240a(18) =965304a(19) =2337409a(20) =5640122a(21) =13637336a(22) =32914794a(23) =79525973a(24) =191966740a(25) =463636600a(26) =1119239940a(27) =2702647921a(28) =6524535782a(29) =15753313808