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A083732
Pseudoprimes to bases 2 and 5.
2
561, 1729, 2821, 5461, 6601, 8911, 12801, 13981, 15841, 29341, 41041, 46657, 52633, 63973, 68101, 75361, 101101, 113201, 115921, 126217, 137149, 162401, 172081, 188461, 252601, 294409, 314821, 334153, 340561, 399001, 401401, 410041, 488881
OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..16699 (terms 1..169 from R. J. Mathar)
FORMULA
a(n) = n-th positive integer k(>1) such that 2^(k-1) = 1 (mod k) and 5^(k-1) = 1 (mod k).
EXAMPLE
a(1)=561 since 561 is the first positive integer k(>1) which satisfies 2^(k-1) = 1 (mod k) and 5^(k-1) = 1 (mod k).
MATHEMATICA
Select[Range[1, 10^5, 2], CompositeQ[#] && PowerMod[2, #-1, #] == PowerMod[5, #-1, #] == 1 &] (* Amiram Eldar, Jun 29 2019 *)
PROG
(PARI) lista(nn) = forcomposite(n=1, nn, if ((Mod(2, n)^(n-1)==1) && (Mod(5, n)^(n-1)==1), print1(n, ", ")); ); \\ Michel Marcus, Sep 08 2016
CROSSREFS
Intersection of A001567 and A005936. - R. J. Mathar, Apr 05 2011
Sequence in context: A321156 A227976 A224930 * A292367 A290805 A217465
KEYWORD
easy,nonn
AUTHOR
Serhat Sevki Dincer (sevki(AT)ug.bilkent.edu.tr), May 05 2003
STATUS
approved