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 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS 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

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Last modified November 23 21:51 EST 2020. Contains 338603 sequences. (Running on oeis4.)