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%I #34 Jun 02 2020 16:02:09
%S 2,20771,40487,41542,80974,83084,161948,643901,1255097,1287802,
%T 1391657,1931703,2510194,2575604,2783314,3765291,3863406,4174971,
%U 5020388,5151208,5566628,7530582,7726812,8349942,10040776,11133256,15061164,15308227,15453624,16699884
%N Numbers n such that 5^A000010(n) == 1 (mod n^2).
%H Giovanni Resta, <a href="/A242959/b242959.txt">Table of n, a(n) for n = 1..479</a> (terms < 10^15, first 75 terms from Felix Fröhlich)
%t Select[Range[167*10^5],PowerMod[5,EulerPhi[#],#^2]==1&] (* _Harvey P. Dale_, Jun 02 2020 *)
%o (PARI) for(n=2, 10^9, if(Mod(5, n^2)^(eulerphi(n))==1, print1(n, ", ")))
%Y Cf. A077816, A242958, A242960.
%Y If a(n) is prime, then a(n) is in A123692.
%K nonn
%O 1,1
%A _Felix Fröhlich_, May 27 2014