G.f.: x^2*(x^2 + x + 1)/(x^4 - 2*x + 1).

Terms

a(0) =1a(1) =3a(2) =7a(3) =14a(4) =27a(5) =51a(6) =95a(7) =176a(8) =325a(9) =599a(10) =1103a(11) =2030a(12) =3735a(13) =6871a(14) =12639a(15) =23248a(16) =42761a(17) =78651a(18) =144663a(19) =266078a(20) =489395a(21) =900139a(22) =1655615a(23) =3045152a(24) =5600909a(25) =10301679a(26) =18947743a(27) =34850334a(28) =64099759a(29) =117897839