A182169 - OEIS

A182169

Numbers n such that sigma(n) divides sum_{k=1..n} tau(k), where tau(k) is the number of divisors of k (A000005) and sigma(n) is the sum of divisors of n (A000203).

1, 2, 7, 19, 358, 3845, 31138, 36461, 4286729, 81945545, 2059172170, 3071920146, 9331669953, 19026491086

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OFFSET

1,2

COMMENTS

a(15) > 5*10^10. - Donovan Johnson, Apr 16 2012

LINKS

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

MATHEMATICA

Select[Range[1000000], Mod[Sum[DivisorSigma[0, n], {n, #}], DivisorSigma[1, #]] == 0 &] (* Jayanta Basu, Mar 28 2013 *)

PROG

(PARI) s=0; for(n=1, 1e6, if((s+=numdiv(n))%sigma(n)==0, print1(n", "))) \\ Charles R Greathouse IV, Apr 16 2012

CROSSREFS

Cf. A006218.

Sequence in context: A054423 A137990 A056650 * A373765 A170869 A162355

Adjacent sequences: A182166 A182167 A182168 * A182170 A182171 A182172

KEYWORD

nonn

AUTHOR

Naohiro Nomoto, Apr 16 2012

EXTENSIONS

a(10) from Charles R Greathouse IV, Apr 16 2012

a(11)-a(14) from Donovan Johnson, Apr 16 2012

STATUS

approved