A053781 Numbers k that divide the sum of the first k composite numbers.

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

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 k such that k divides A053767(k). - 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 A137767

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