a(0) = 1, a(1) = -4, a(n) = -4*a(n-1) - a(n-2) for n > 1.

Terms

a(0) =1a(1) =-4a(2) =15a(3) =-56a(4) =209a(5) =-780a(6) =2911a(7) =-10864a(8) =40545a(9) =-151316a(10) =564719a(11) =-2107560a(12) =7865521a(13) =-29354524a(14) =109552575a(15) =-408855776a(16) =1525870529a(17) =-5694626340a(18) =21252634831a(19) =-79315912984a(20) =296011017105