a(n) = - 4*a(n-2) - a(n-4), a(0) = 1, a(1) = -4, a(2) = -6, a(3) = 15.

Terms

a(0) =1a(1) =-4a(2) =-6a(3) =15a(4) =23a(5) =-56a(6) =-86a(7) =209a(8) =321a(9) =-780a(10) =-1198a(11) =2911a(12) =4471a(13) =-10864a(14) =-16686a(15) =40545a(16) =62273a(17) =-151316a(18) =-232406a(19) =564719a(20) =867351a(21) =-2107560a(22) =-3236998a(23) =7865521a(24) =12080641a(25) =-29354524a(26) =-45085566a(27) =109552575a(28) =168261623a(29) =-408855776