a(n)= 5*a(n-1) -a(n-2) -a(n-3).

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =13a(5) =61a(6) =289a(7) =1371a(8) =6505a(9) =30865a(10) =146449a(11) =694875a(12) =3297061a(13) =15643981a(14) =74227969a(15) =352198803a(16) =1671122065a(17) =7929183553a(18) =37622596897a(19) =178512678867a(20) =847011613885