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%I #18 Jan 15 2024 12:21:02
%S 1,2,3,4,5,7,8,9,11,13,15,16,17,18,19,21,23,25,27,29,31,32,33,35,37,
%T 39,41,43,45,47,49,50,51,53,55,57,59,61,64,65,67,69,71,72,73,77,79,81,
%U 83,85,87,89,91,93,95,97,98,99,100,101,103,105,107,109,111,113,115,119
%N Numbers k such that k and sum of 4th powers of divisors of k are relatively prime.
%C All even terms are either squares or doubled squares. - _Ivan Neretin_, Dec 30 2015
%C The asymptotic density of this sequence is 0 (Dressler, 1974). - _Amiram Eldar_, Jul 23 2020
%H Ivan Neretin, <a href="/A046687/b046687.txt">Table of n, a(n) for n = 1..10076</a>
%H Robert E. Dressler, <a href="https://doi.org/10.4153/CMB-1974-019-5">On a theorem of Niven</a>, Canadian Mathematical Bulletin, Vol. 17, No. 1 (1974), pp. 109-110.
%t Select[Range[120], GCD[#, DivisorSigma[4, #]] == 1 &] (* _Ivan Neretin_, Dec 30 2015 *)
%t Select[Range[150],CoprimeQ[#,DivisorSigma[4,#]]&] (* _Harvey P. Dale_, Jan 15 2024 *)
%o (PARI) isok(n) = gcd(n, sigma(n, 4)) == 1; \\ _Michel Marcus_, Dec 20 2013
%Y Cf. A001159, A046684, A046686.
%K nonn
%O 1,2
%A _Labos Elemer_
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