a(n) = 3*a(n-1) + a(n-2), with a(0)=7, a(1)=26.

Terms

a(0) =7a(1) =26a(2) =85a(3) =281a(4) =928a(5) =3065a(6) =10123a(7) =33434a(8) =110425a(9) =364709a(10) =1204552a(11) =3978365a(12) =13139647a(13) =43397306a(14) =143331565a(15) =473392001a(16) =1563507568a(17) =5163914705a(18) =17055251683a(19) =56329669754a(20) =186044260945a(21) =614462452589