A390081 Numbers k such that the abundancy index of k is equal to the abundancy index of d(k).

1, 2, 28, 234, 174592

Offset

1,2

Comments

The corresponding number of divisors are: 1, 2, 6, 12, 40.

Links

Table of n, a(n) for n=1..5.

Michel Marcus, solveBA PARI script

Prog

(PARI) isok(k) = sigma(k, -1) == sigma(numdiv(k), -1);
(PARI) lista(nn, lim) = for (n=1, nn, my(ad = sigma(n, -1), v = solveBA(numerator(ad), denominator(ad), lim)); if (#v, my(vn = apply(numdiv, v), vs = select(x->x==n, vn, 1)); if (#vs, print1(v[vs[1]], ", ")); ); ); \\ using solveBA script
lista(10000, 10^30)

Crossrefs

Cf. A000005, A392506.

Sequence in context: A035601 A281124 A244721 * A001759 A243475 A019441

Adjacent sequences: A390078 A390079 A390080 * A390082 A390083 A390084

Keyword

nonn,more

Author

Michel Marcus, Jan 15 2026

Status

approved