1,1

By pure convention, we could include a leading 1 to this sequence, as someone using the mathematically arguably value A006530(1) = 1 might search for this sequence with a leading 1. However, this was not done in view of the age of this sequence. - Rémy Sigrist, Jan 09 2018

In contrast to A388275\{1}, which is a subsequence of this, powerful terms (A001694) are readily found here: 1372, 10976, 37044, 296352, 3301489, 3775249, 6145441, 13205956, ..., - Antti Karttunen, Sep 21 2025

Antti Karttunen, Table of n, a(n) for n = 1..10000 (first 1000 terms from Michel Marcus)

Index entries for sequences related to sigma(n).

Index entries for sequences where odd perfect numbers must occur, if they exist at all.

n such that A006530(n) = A006530(sigma(n)).

n such that A006530(n) = A071190(n). - Michel Marcus, Oct 11 2017

1550 = 2*5^2*31 and sigma(1550) = 2976 = 2^5*3*31 hence 1550 is in the sequence.

fQ[n_] := FactorInteger[n][[-1, 1]] == FactorInteger[DivisorSigma[1, n]][[-1, 1]]; Rest@ Select[ Range@3500, fQ] (* Robert G. Wilson v, Jan 09 2018 *)

(PARI) for(n=2, 1000, if(component(component(factor(n), 1), omega(n)) == component(component(factor(sigma(n)), 1), omega(sigma(n))), print1(n, ", ")))

(PARI) isok(n) = vecmax(factor(n)[, 1]) == vecmax(factor(sigma(n))[, 1]); \\ Michel Marcus, Sep 29 2017

Cf. A000203 (sigma), A006530 (gpf), A071190.

Subsequences: A000396 (perfect numbers), A005820, most likely the whole A007691, A388275\{1}.

Sequence in context: A242344 A344588 A247111 * A388275 A295078 A055196

Adjacent sequences: A071831 A071832 A071833 * A071835 A071836 A071837

easy,nonn

Benoit Cloitre, Jun 08 2002

approved