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

Terms

a(0) =1a(1) =2a(2) =11a(3) =50a(4) =233a(5) =1082a(6) =5027a(7) =23354a(8) =108497a(9) =504050a(10) =2341691a(11) =10878914a(12) =50540729a(13) =234799658a(14) =1090820819a(15) =5067682250a(16) =23543191457a(17) =109375812578a(18) =508132824683