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

Terms

a(0) =1a(1) =1a(2) =1a(3) =-4a(4) =6a(5) =-9a(6) =16a(7) =-29a(8) =51a(9) =-89a(10) =156a(11) =-274a(12) =481a(13) =-844a(14) =1481a(15) =-2599a(16) =4561a(17) =-8004a(18) =14046a(19) =-24649a(20) =43256a(21) =-75909a(22) =133211a(23) =-233769a(24) =410236a(25) =-719914a(26) =1263361a(27) =-2217044a(28) =3890641a(29) =-6827599