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

Terms

a(0) =3a(1) =4a(2) =24a(3) =88a(4) =360a(5) =1432a(6) =5736a(7) =22936a(8) =91752a(9) =367000a(10) =1468008a(11) =5872024a(12) =23488104a(13) =93952408a(14) =375809640a(15) =1503238552a(16) =6012954216a(17) =24051816856a(18) =96207267432a(19) =384829069720