a(n) = 2*a(n-1) + a(n-2) for n > 1; a(0) = 3, a(1) = 11.

Terms

a(0) =3a(1) =11a(2) =25a(3) =61a(4) =147a(5) =355a(6) =857a(7) =2069a(8) =4995a(9) =12059a(10) =29113a(11) =70285a(12) =169683a(13) =409651a(14) =988985a(15) =2387621a(16) =5764227a(17) =13916075a(18) =33596377a(19) =81108829a(20) =195814035a(21) =472736899a(22) =1141287833a(23) =2755312565a(24) =6651912963a(25) =16059138491a(26) =38770189945a(27) =93599518381