a(n) = 3*a(n-1)-4*a(n-3)+a(n-4)+a(n-5)+3*a(n-6)-a(n-7) for n >= 8, with initial values as shown.

Terms

a(0) =2a(1) =3a(2) =6a(3) =14a(4) =34a(5) =84a(6) =208a(7) =515a(8) =1272a(9) =3138a(10) =7734a(11) =19055a(12) =46940a(13) =115631a(14) =284846a(15) =701709a(16) =1728662a(17) =4258604a(18) =10491218a(19) =25845514a(20) =63671404a(21) =156856887a(22) =386422704a(23) =951966378a(24) =2345203554a(25) =5777493461a(26) =14233063160a(27) =35063663603a(28) =86380598122a(29) =212801715171