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A083736 Pseudoprimes to bases 2,5 and 7. 1
561, 29341, 46657, 75361, 115921, 162401, 252601, 294409, 314821, 334153, 340561, 399001, 410041, 488881, 512461, 530881, 552721, 656601, 658801, 710533, 721801, 852841, 1024651, 1141141, 1152271, 1168513, 1193221, 1461241, 1569457, 1615681 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..8691 (terms 1..81 from R. J. Mathar)

F. Richman, Primality testing with Fermat's little theorem

FORMULA

a(n) = n-th positive integer k(>1) such that 2^(k-1) = 1 (mod k), 5^(k-1) = 1 (mod k) and 7^(k-1) = 1 (mod k).

EXAMPLE

a(1)=561 since it is the first number such that 2^(k-1) = 1 (mod k), 5^(k-1) = 1 (mod k) and 7^(k-1) = 1 (mod k).

MATHEMATICA

Select[Range[1, 10^5, 2], CompositeQ[#] &&  PowerMod[2, #-1, #] == PowerMod[5, #-1, #] == PowerMod[7, #-1, #] == 1&] (* Amiram Eldar, Jun 29 2019 *)

CROSSREFS

Intersection of A083732 and A005938. Intersection of A083733 and A005936. - R. J. Mathar, Apr 05 2011

Sequence in context: A232761 A232755 A264214 * A182090 A006931 A258801

Adjacent sequences:  A083733 A083734 A083735 * A083737 A083738 A083739

KEYWORD

easy,nonn

AUTHOR

Serhat Sevki Dincer (sevki(AT)ug.bilkent.edu.tr), May 05 2003

STATUS

approved

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Last modified February 20 15:52 EST 2020. Contains 332078 sequences. (Running on oeis4.)