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 A063986 Numbers n such that n divides Sum_{k=1..n} A051953(k) where A051953(k)=k-Phi(k). Arithmetic mean of first n cototient values is an integer. 6
 1, 4, 5, 24, 25, 249, 600, 617, 12272, 13763, 21332, 25228, 783665, 15748051, 41846733, 195853251, 2488541984, 14399065016, 21119309213, 22430204140, 43787603128, 157825075944, 206651865067, 271605149320, 374049315076, 650288309748 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The odd terms of A048290 and A063986 are the same. - Jud McCranie, Jun 26 2005 a(27) > 10^12. - Donovan Johnson, Dec 09 2011 LINKS EXAMPLE n=5: (1 + 1 + 2 + 2 + 4)/5 = 2. MATHEMATICA s = 0; Do[s = s + n - EulerPhi[n]; If[ IntegerQ[s/n], Print[n]], {n, 1, 10^7} ] CROSSREFS Cf. A051953, A000010, A002088, A048920, A000217, A050226. Sequence in context: A338422 A171885 A331261 * A039583 A042123 A041531 Adjacent sequences:  A063983 A063984 A063985 * A063987 A063988 A063989 KEYWORD nonn AUTHOR Labos Elemer, Sep 06 2001 EXTENSIONS More terms from Dean Hickerson, Sep 07 2001 One more term from Robert G. Wilson v, Sep 07 2001 a(16) and a(17) from Jud McCranie, Jun 22 2005 a(18)-a(21) from Donovan Johnson, May 11 2010 a(22)-a(26) from Donovan Johnson, Dec 09 2011 STATUS approved

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Last modified May 15 20:38 EDT 2021. Contains 343920 sequences. (Running on oeis4.)