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A063986 Numbers k that divide Sum_{j=1..k} A051953(j) where A051953(j) = j - Phi(j). Arithmetic mean of first k cototient values is an integer.

%I A063986 #22 Aug 20 2021 22:48:57
%S A063986 1,4,5,24,25,249,600,617,12272,13763,21332,25228,783665,15748051,
%T A063986 41846733,195853251,2488541984,14399065016,21119309213,22430204140,
%U A063986 43787603128,157825075944,206651865067,271605149320,374049315076,650288309748
%N A063986 Numbers k that divide Sum_{j=1..k} A051953(j) where A051953(j) = j - Phi(j). Arithmetic mean of first k cototient values is an integer.
%C A063986 The odd terms of A048290 and A063986 are the same. - _Jud McCranie_, Jun 26 2005
%C A063986 a(27) > 10^12. - _Donovan Johnson_, Dec 09 2011
%e A063986 k=5: (1 + 1 + 2 + 2 + 4)/5 = 2.
%t A063986 s = 0; Do[s = s + n - EulerPhi[n]; If[ IntegerQ[s/n], Print[n]], {n, 1, 10^7} ]
%Y A063986 Cf. A051953, A000010, A002088, A048920, A000217, A050226.
%K A063986 nonn
%O A063986 1,2
%A A063986 _Labos Elemer_, Sep 06 2001
%E A063986 More terms from _Dean Hickerson_, Sep 07 2001
%E A063986 One more term from _Robert G. Wilson v_, Sep 07 2001
%E A063986 a(16) and a(17) from _Jud McCranie_, Jun 22 2005
%E A063986 a(18)-a(21) from _Donovan Johnson_, May 11 2010
%E A063986 a(22)-a(26) from _Donovan Johnson_, Dec 09 2011