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%I #19 Feb 17 2024 10:32:40
%S 1,3,4,5,7,11,12,13,15,16,17,19,20,21,23,25,27,28,29,31,33,35,37,39,
%T 41,43,44,47,48,49,51,52,53,55,57,59,60,61,65,67,68,69,71,73,75,76,77,
%U 79,80,81,83,84,85,87,89,91,92,93,95,97,100,101,103,105,107,108,109,111
%N Number of divisors divides sum of 4th powers of divisors.
%C A020486 is very similar to this sequence, but it does not include the following values below 1000 (which this sequence does include): {16, 80, 81, 176, 304, 324, 400, 405, 464, 496, 656, 784, 880, 891, 944, 976}.
%H T. D. Noe, <a href="/A046840/b046840.txt">Table of n, a(n) for n = 1..1000</a>
%e x=16 with 5 divisors, sigma(k,16) = 5, 31, 341, 46801, 69905 for k=0,1,2,3,4, respectively. It is seen that sigma(4,16) = 13981*sigma(0,64) = 41*sigma(2,64)*sigma(0,64).
%o (Magma) [n: n in [1..120] | IsZero(DivisorSigma(4, n) mod NumberOfDivisors(n))]; // _Bruno Berselli_, Apr 11 2013
%o (PARI) isok(n) = sigma(n, 4) % numdiv(n) == 0; \\ _Michel Marcus_, May 13 2018
%Y Cf. A020486, A003601.
%K nonn
%O 1,2
%A _Labos Elemer_
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