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 A006970 Euler pseudoprimes: 2^((n-1)/2) == +- 1 mod n. (Formerly M5442) 11
 341, 561, 1105, 1729, 1905, 2047, 2465, 3277, 4033, 4681, 5461, 6601, 8321, 8481, 10261, 10585, 12801, 15709, 15841, 16705, 18705, 25761, 29341, 30121, 31621, 33153, 34945, 41041, 42799 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Pseudoprimes for the primality test from [Schick]: n odd is probably prime if (n-1) | A003558((n-1)/2). (Succeeds for 99.9975% of odd natural numbers less than 10^8.) - Jonathan Skowera, Jun 29 2013 REFERENCES R. K. Guy, Unsolved Problems in Number Theory, A12. C. Schick, Weiche Primzahlen und das 257-Eck, 2008, pages 140-146. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Eric Weisstein's World of Mathematics, Euler Pseudoprime. MATHEMATICA 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] (* Jean-François Alcover, Apr 06 2011 *) PROG (PARI) isok(n) = {if (!isprime(n) && (n%2), npm = Mod(2, n)^((n-1)/2); if ((npm == Mod(1, n)) || (npm == Mod(-1, n)), print1(n, ", ")); ); } \\ Michel Marcus, Sep 12 2015 CROSSREFS Sequence in context: A001567 A178723 A210993 * A007324 A007011 A064907 Adjacent sequences:  A006967 A006968 A006969 * A006971 A006972 A006973 KEYWORD nonn,nice AUTHOR EXTENSIONS a(15) corrected (to 10261 from 10241) by Faron Moller (fm(AT)csd.uu.se) STATUS approved

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