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%I #17 Mar 03 2020 09:00:43
%S 28,140,190,248,420,477,496,672,840,910,1428,1488,1547,1638,1848,1892,
%T 2295,2398,2480,2660,3417,3472,3515,3640,3720,4064,4095,4590,4641,
%U 4655,4845,5456,5655,5995,6200,6678,6888,6944,7030,7440,8008,8128,8190,9214,9282
%N Numbers k such that sigma(k) divides the sum of the numbers x coprime to k, with x <= k.
%C Numbers k such that sigma(k) | k*phi(k)/2.
%H Amiram Eldar, <a href="/A239205/b239205.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..500 from Paolo P. Lava)
%e 28 is a term since 28*phi(28)/2 = 168, sigma(28) = 56 and 168 / 56 = 3.
%p with(numtheory); P:=proc(q) local a,n;
%p for n from 1 to q do a:=n*phi(n)/2; if type(a/sigma(n),integer) then print(n);
%p fi; od; end: P(10^6);
%t Select[Range[10^4], Divisible[# * EulerPhi[#]/2, DivisorSigma[1, #]] &] (* _Amiram Eldar_, Mar 03 2020 *)
%Y Cf. A000010, A000203, A238232, A239208.
%K nonn,easy
%O 1,1
%A _Paolo P. Lava_, Mar 12 2014
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