

A053781


Numbers n such that n divides sum of first n composite numbers.


4



1, 2, 3, 7, 11, 71, 107, 115, 139, 155, 681, 1671, 4876, 21464, 30046, 311271, 788749, 10893662, 20743270, 134568163, 163879554, 920161004, 6364787032, 21400458779, 47934932406, 56133884369, 288050185452, 536023681676, 1484061538595
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OFFSET

1,2


LINKS

Table of n, a(n) for n=1..29.
E. Friedman, What is special about this number?, see 681.


FORMULA

Numbers n such that n divides A053767(n).  Robert G. Wilson v, Nov 24 2004


MATHEMATICA

c = s = 0; Do[ If[ !PrimeQ[n], c++; s = s + n; If[ Mod[s, c] == 0, Print[c]]], {n, 2, 10^9}] (* Robert G. Wilson v, Nov 23 2004 *)


PROG

(PARI) lista(nn) = {s = 0; n = 0; forcomposite(c=0, nn, s += c; n++; if (! (s % n), print1(n, ", ")); ); } \\ Michel Marcus, Mar 15 2015


CROSSREFS

Cf. A002808, A073262, A073263.
Sequence in context: A175171 A073609 A267091 * A066749 A306786 A046480
Adjacent sequences: A053778 A053779 A053780 * A053782 A053783 A053784


KEYWORD

nonn


AUTHOR

G. L. Honaker, Jr., Mar 29 2000


EXTENSIONS

a(19)a(22) from Robert G. Wilson v, Nov 24 2004
a(23)a(26) from Sean A. Irvine, Oct 01 2009
a(27)a(29) from Donovan Johnson, Jul 06 2010


STATUS

approved



