G.f.: exp( Sum_{n>=1} sigma(2n)*x^n/n ).

Terms

a(0) =1a(1) =3a(2) =8a(3) =19a(4) =41a(5) =83a(6) =161a(7) =299a(8) =538a(9) =942a(10) =1610a(11) =2694a(12) =4427a(13) =7153a(14) =11387a(15) =17884a(16) =27741a(17) =42543a(18) =64565a(19) =97034a(20) =144519a(21) =213432a(22) =312720a(23) =454803a(24) =656835a(25) =942364a(26) =1343596a(27) =1904354a(28) =2684008a(29) =3762667