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%I #10 May 14 2021 13:48:30
%S 1897121,52368101,126233057
%N Odd primes p such that ((p+1)/2)^(p-1) == 1 (mod p^2).
%C The corresponding sequence when (p+1) in the congruence is replaced with (p-1) seems to be A125854.
%C a(4) > 4262937421 if it exists.
%t Select[Prime[Range[718*10^4]],PowerMod[(#+1)/2,#-1,#^2]==1&] (* _Harvey P. Dale_, May 14 2021 *)
%o (PARI) forprime(p=3, , my(x=(p+1)/2); if(Mod(x, p^2)^(p-1)==1, print1(p, ", ")))
%Y Cf. A125854, A259502.
%K nonn,hard,bref,more
%O 1,1
%A _Felix Fröhlich_, Jan 24 2019