G.f.: (x+2)*(x+1)/((x-1)*(x-2)) = Sum_{n>=0} a(n)*(x/2)^n.

Terms

a(0) =1a(1) =3a(2) =9a(3) =21a(4) =45a(5) =93a(6) =189a(7) =381a(8) =765a(9) =1533a(10) =3069a(11) =6141a(12) =12285a(13) =24573a(14) =49149a(15) =98301a(16) =196605a(17) =393213a(18) =786429a(19) =1572861a(20) =3145725a(21) =6291453a(22) =12582909a(23) =25165821a(24) =50331645a(25) =100663293a(26) =201326589a(27) =402653181a(28) =805306365a(29) =1610612733