G.f.: Sum( x^k/(1-2*x+x^k), k=1..oo).

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =7a(5) =12a(6) =20a(7) =34a(8) =58a(9) =101a(10) =178a(11) =318a(12) =574a(13) =1046a(14) =1920a(15) =3548a(16) =6593a(17) =12312a(18) =23092a(19) =43480a(20) =82154a(21) =155716a(22) =295984a(23) =564050a(24) =1077400a(25) =2062311a(26) =3955186a(27) =7598756a(28) =14622318a(29) =28179338