a(n) = Sum_{k=0..n-1} sigma(2k+1)*sigma_3(n-k).

Terms

a(0) =1a(1) =13a(2) =70a(3) =247a(4) =671a(5) =1547a(6) =3178a(7) =5916a(8) =10317a(9) =17088a(10) =26818a(11) =40703a(12) =60034a(13) =85463a(14) =119288a(15) =163736a(16) =218924a(17) =288933a(18) =377482a(19) =482734a(20) =612535a(21) =772291a(22) =955604a(23) =1177050a(24) =1443522a(25) =1742481a(26) =2097702a(27) =2517368a(28) =2978851a(29) =3519151