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A083735 Pseudoprimes to bases 3 and 7. 3
703, 1105, 2465, 10585, 18721, 19345, 29341, 38503, 46657, 50881, 75361, 76627, 88831, 104653, 115921, 146611, 162401, 188191, 213265, 226801, 252601, 278545, 286903, 294409, 314821, 334153, 340561, 359341, 385003, 385201, 399001, 410041 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..16479 (terms 1..151 from R. J. Mathar)

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

Index entries for sequences related to pseudoprimes

FORMULA

a(n) = n-th positive integer k(>1) such that 3^(k-1) = 1 (mod k) and 7^(k-1) = 1 (mod k).

EXAMPLE

a(1)=703 since it is the first number such that 3^(k-1) = 1 (mod k) and 7^(k-1) = 1 (mod k).

MATHEMATICA

Select[Range[420000], !PrimeQ[#]&&PowerMod[3, #-1, #]==1&&PowerMod[7, #-1, #] == 1&] (* Harvey P. Dale, Mar 08 2014 *)

PROG

(PARI) is(n)=!isprime(n)&&Mod(7, n)^(n-1)==1&&Mod(3, n)^(n-1)==1 \\ Charles R Greathouse IV, Apr 12 2012

CROSSREFS

Intersection of A005935 and A005938. - R. J. Mathar, Apr 05 2011

Sequence in context: A035852 A214486 A045146 * A161021 A283521 A257721

Adjacent sequences:  A083732 A083733 A083734 * A083736 A083737 A083738

KEYWORD

nonn

AUTHOR

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

STATUS

approved

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Last modified February 22 14:33 EST 2020. Contains 332136 sequences. (Running on oeis4.)