a(n) = 3*a(n-1) + a(n-2), with a(0)=4, a(1)=11.

Terms

a(0) =4a(1) =11a(2) =37a(3) =122a(4) =403a(5) =1331a(6) =4396a(7) =14519a(8) =47953a(9) =158378a(10) =523087a(11) =1727639a(12) =5706004a(13) =18845651a(14) =62242957a(15) =205574522a(16) =678966523a(17) =2242474091a(18) =7406388796a(19) =24461640479a(20) =80791310233a(21) =266835571178a(22) =881298023767