a(n) = 2*a(n-1) - a(n-2) - a(n-4).

Terms

a(0) =1a(1) =1a(2) =1a(3) =-1a(4) =-4a(5) =-8a(6) =-13a(7) =-17a(8) =-17a(9) =-9a(10) =12a(11) =50a(12) =105a(13) =169a(14) =221a(15) =223a(16) =120a(17) =-152a(18) =-645a(19) =-1361a(20) =-2197a(21) =-2881a(22) =-2920a(23) =-1598a(24) =1921a(25) =8321a(26) =17641a(27) =28559a(28) =37556a(29) =38232