|
%I #18 Jun 12 2021 22:40:56
%S 2,3,5,10,33,55,82,129,136,145,261,351,385,406,442,513,649,897,1090,
%T 2241,4726,5185,8650,13601,17101,17641,18241,26625,26937,29697,29953,
%U 32896,34561,35841,38417,44955,46081,46593,51985,63505,65703,66249,84376,93313,97903
%N Numbers k such that sigma(k)^2 is divisible by k-1.
%e For k=10, sigma(10)^2 / (10-1) = 18^2 / 9 = 324 / 9 = 36.
%t Select[Range[2, 10^5], Divisible[DivisorSigma[1, #]^2, # - 1] &] (* _Amiram Eldar_, May 15 2021 *)
%o (PARI)
%o list(nn) = for(n=2, nn, if (sigma(n)^2 % (n-1) == 0, print1(n, ", ")))
%o list(100000)
%Y Cf. A072861, A263928.
%K nonn
%O 1,1
%A _Zdenek Cervenka_, May 15 2021
|
