a(n) = binomial(sigma(n), n).

Terms

a(0) =1a(1) =3a(2) =4a(3) =35a(4) =6a(5) =924a(6) =8a(7) =6435a(8) =715a(9) =43758a(10) =12a(11) =30421755a(12) =14a(13) =1961256a(14) =1307504a(15) =300540195a(16) =18a(17) =62359143990a(18) =20a(19) =513791607420a(20) =129024480a(21) =3796297200a(22) =24a(24) =736281a(25) =166509721602a(26) =12033222880a(28) =30