G.f.: -x*(1+x+x^2+2*x^3+3*x^4+3*x^5+x^6-x^7-x^9)/((1+x)*(-1+2*x+x^3)).

Terms

a(0) =0a(1) =1a(2) =2a(3) =5a(4) =12a(5) =28a(6) =62a(7) =136a(8) =299a(9) =661a(10) =1456a(11) =3213a(12) =7085a(13) =15628a(14) =34467a(15) =76021a(16) =167668a(17) =369805a(18) =815629a(19) =1798928a(20) =3967659a(21) =8750949a(22) =19300824a(23) =42569309a(24) =93889565a(25) =207079956a(26) =456729219a(27) =1007348005a(28) =2221775964a(29) =4900281149