G.f.: 1 / ( (1 + x^2 - x^3)^2 * (1 - x - 2*x^2 - x^3) ).

Terms

a(0) =1a(1) =1a(2) =1a(3) =6a(4) =12a(5) =19a(6) =48a(7) =110a(8) =218a(9) =470a(10) =1040a(11) =2208a(12) =4710a(13) =10184a(14) =21879a(15) =46879a(16) =100767a(17) =216570a(18) =464952a(19) =998613a(20) =2145312a(21) =4607724a(22) =9896436a(23) =21257196a(24) =45658624a(25) =98068864a(26) =210642412a(27) =452440320a(28) =971794317a(29) =2087314717