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

Terms

a(0) =1a(1) =7a(2) =32a(3) =119a(4) =385a(5) =1127a(6) =3057a(7) =7799a(8) =18914a(9) =43950a(10) =98434a(11) =213486a(12) =450051a(13) =925013a(14) =1858355a(15) =3657052a(16) =7062245a(17) =13404195a(18) =25038741a(19) =46086250a(20) =83669927a(21) =149970936a(22) =265608168a(23) =465149039a(24) =806022315a(25) =1382822644a(26) =2350101516a(27) =3958427938