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 A006970 Euler pseudoprimes: 2^{(n-1)/2} == +- 1 mod n. (Formerly M5442) 2

%I M5442

%S 341,561,1105,1729,1905,2047,2465,3277,4033,4681,5461,6601,8321,8481,

%T 10261,10585,12801,15709,15841,16705,18705,25761,29341,30121,31621,

%U 33153,34945,41041,42799

%N Euler pseudoprimes: 2^{(n-1)/2} == +- 1 mod n.

%D R. K. Guy, Unsolved Problems in Number Theory, A12.

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%H T. D. Noe, <a href="/A006970/b006970.txt">Euler pseudoprimes up to 10^8; table of n, a(n) for n = 1..1231</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/EulerPseudoprime.html">Euler Pseudoprime.</a>

%H <a href="/index/Ps#pseudoprimes">Index entries for sequences related to pseudoprimes</a>

%t ok[_?PrimeQ] = False; ok[n_] := (p = PowerMod[2, (n - 1)/2, n]; p == Mod[1, n] || p == Mod[-1, n]); Select[2 Range[22000] + 1, ok] (* From Jean-François Alcover, Apr 06 2011 *)

%K nonn,nice

%O 1,1

%A _N. J. A. Sloane_, _Robert G. Wilson v_, rgep(AT)chalcedon.demon.co.uk

%E Faron Moller (fm(AT)csd.uu.se) corrected the 15th entry to 10261 from 10241.

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