%I #37 Jun 29 2019 10:19:05
%S 217,781,1541,1729,5461,5611,6601,7449,7813,11041,12801,13021,13333,
%T 14981,15751,15841,16297,21361,23653,24211,25351,29539,30673,38081,
%U 40501,41041,44173,44801,46657,47641,48133,53971,56033,67921,75361,79381,90241,98173,100651,102311
%N Euler pseudoprimes to base 5: composite integers such that abs(5^((n - 1)/2)) == 1 mod n.
%H Amiram Eldar, <a href="/A262052/b262052.txt">Table of n, a(n) for n = 1..10000</a> (term 1..65 from Daniel Lignon)
%t eulerPseudoQ[n_?PrimeQ, b_] = False; eulerPseudoQ[n_, b_] := Block[{p = PowerMod[b, (n - 1)/2, n]}, p == Mod[1, n] || p == Mod[-1, n]]; Select[2 Range[27000] + 1, eulerPseudoQ[#, 5] &] (* _Michael De Vlieger_, Sep 09 2015, after _Jean-François Alcover_ at A006970 *)
%o (PARI) for(n=1, 1e5, if( Mod(5, (2*n+1))^n == 1 || Mod(5, (2*n+1))^n == 2*n && bigomega(2*n+1) != 1 , print1(2*n+1", "))); \\ _Altug Alkan_, Oct 11 2015
%Y Cf. A006970 (base 2), A262051 (base 3), this sequence (base 5), A262053 (base 6), A262054 (base 7), A262055 (base 8).
%K nonn
%O 1,1
%A _Daniel Lignon_, Sep 09 2015