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A168127 Numbers k such that sum_(k=1...n) sigma(k) / sigma (k) is an integer. 4
1, 3, 29, 365, 1225, 81595, 86249, 185699, 582917, 11413204, 16646745763, 311408527843, 709342670921, 881267828693 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers k such that A024916(k) / A000203(k) is an integer.

Corresponding values of sigma (k), sum_(k=1...n) sigma(k) and sum_(k=1...n) sigma(k)/sigma(k) are given in A168129, A168130 and A168128. - Jaroslav Krizek, Nov 21 2009

a(11) > 10^10. - Donovan Johnson, Oct 16 2013

a(15) > 10^12. - Giovanni Resta, Jun 06 2016

LINKS

Table of n, a(n) for n=1..14.

EXAMPLE

Number a(3) = 29 is in sequence because A024916(29) / A000203(29) = 690 / 30 = 23 is an integer.

PROG

(PARI) m=0; for(k=1, 11413204, s=sigma(k); m=m+s; if(m%s==0, print1(k ", "))) \\ Donovan Johnson, Oct 16 2013

CROSSREFS

Cf. A000203, A024916, A168128, A168129, A168130.

Sequence in context: A049038 A091646 A081506 * A262640 A302582 A302923

Adjacent sequences:  A168124 A168125 A168126 * A168128 A168129 A168130

KEYWORD

nonn,more

AUTHOR

Jaroslav Krizek, Nov 18 2009, Dec 04 2009

EXTENSIONS

a(8)-a(10) from Donovan Johnson, Oct 16 2013

a(11)-a(14) from Giovanni Resta, Jun 06 2016

STATUS

approved

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Last modified October 15 17:24 EDT 2019. Contains 328037 sequences. (Running on oeis4.)