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

Terms

a(0) =1a(1) =3a(2) =6a(3) =21a(4) =15a(5) =66a(6) =28a(7) =1365a(8) =1716a(9) =3060a(10) =66a(11) =20475a(12) =91a(13) =134596a(14) =735471a(15) =7888725a(16) =153a(17) =3262623a(18) =190a(19) =118030185a(20) =225792840a(21) =254186856a(22) =276a(23) =2558620845a(24) =84672315a(25) =11058116888a(26) =113380261800a(27) =558383307300a(28) =435a(29) =11969016345