G.f.: Sum_{n>=1} Pell(n+1) * x^n / (1 - x^n), where Pell(n) = A000129(n).

Terms

a(0) =2a(1) =7a(2) =14a(3) =36a(4) =72a(5) =188a(6) =410a(7) =1021a(8) =2392a(9) =5818a(10) =13862a(11) =33678a(12) =80784a(13) =195440a(14) =470916a(15) =1137710a(16) =2744212a(17) =6627675a(18) =15994430a(19) =38619812a(20) =93222780a(21) =225072548a(22) =543339722a(23) =1311772784a(24) =3166816034a(25) =7645450834a(26) =18457558444a(27) =44560677618a(28) =107578520352a(29) =259717999680