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

Terms

a(0) =0a(1) =1a(2) =2a(3) =7a(4) =20a(5) =61a(6) =182a(7) =547a(8) =1640a(9) =4921a(10) =14762a(11) =44287a(12) =132860a(13) =398581a(14) =1195742a(15) =3587227a(16) =10761680a(17) =32285041a(18) =96855122a(19) =290565367a(20) =871696100a(21) =2615088301a(22) =7845264902a(23) =23535794707a(24) =70607384120a(25) =211822152361a(26) =635466457082