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

Terms

a(0) =1a(1) =1a(2) =2a(3) =2a(4) =4a(5) =5a(6) =10a(7) =16a(8) =32a(9) =61a(10) =127a(11) =270a(12) =600a(13) =1378a(14) =3274a(15) =8021a(16) =20245a(17) =52535a(18) =140014a(19) =382745a(20) =1072025a(21) =3073443a(22) =9010934a(23) =26994231a(24) =82563483a(25) =257634875a(26) =819648796a(27) =2656956702a(28) =8770406923a(29) =29464217659