A328174 a(n) is the least integer k such that sigma(k)/(d(k)*sopf(k)) = n where d=A000005, sigma=A000203 and sopf=A008472.

20, 140, 54, 189, 378, 1365, 540, 945, 1120, 1755, 1539, 3465, 500, 1815, 4256, 6384, 14645, 5280, 1323, 1029, 864, 23871, 34579, 12903, 1715, 2673, 11934, 5589, 106805, 12285, 5600, 11625, 21070, 41915, 4459, 16905, 61320, 6615, 11178, 5145, 110839, 19656, 109225

Offset: 1

Author

Michel Marcus, Oct 06 2019

Keywords

• nonn

Crossrefs

Cf. A000005, A000203, A008472, A134382, A328051, A328052, A328175.

Programs

PARI

sopf(f) = sum(j=1, #f~, f[j, 1]); \\ A008472
isok(k, n) = my(fk=factor(k)); n*numdiv(fk)*sopf(fk) == sigma(fk);
a(n) = {my(k=1); while (!isok(k, n), k++); k;}