G.f.: exp( Sum_{n>=1} (x^n/n)/sqrt(1 - 4*x^n) ).

Terms

a(0) =1a(1) =1a(2) =3a(3) =9a(4) =32a(5) =114a(6) =431a(7) =1633a(8) =6306a(9) =24466a(10) =95604a(11) =374920a(12) =1475731a(13) =5822941a(14) =23027817a(15) =91225983a(16) =361945480a(17) =1437855016a(18) =5718242653a(19) =22762417519a(20) =90684186378a(21) =361540944078