1,3

Michel Marcus, Table of n, a(n) for n = 1..130

a(n) = A007814(A019278(n)).

(PARI) lista(nn) = for (n=1, nn, if (denominator(sigma(sigma(n))/n) == 1, print1(valuation(n, 2), ", ")); ); \\ Michel Marcus, Oct 10 2017

Cf. A007814, A019278, A205597 (when a(n) is zero).

Cf. A134665 (analog for multiperfect numbers).

Sequence in context: A324906 A164917 A166238 * A014197 A181308 A292246

Adjacent sequences: A293272 A293273 A293274 * A293276 A293277 A293278

nonn

Michel Marcus, Oct 10 2017

approved