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A083732
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Pseudoprimes to bases 2 and 5.
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2
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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
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OFFSET
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1,1
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LINKS
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FORMULA
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a(n) = n-th positive integer k(>1) such that 2^(k-1) = 1 (mod k) and 5^(k-1) = 1 (mod k).
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EXAMPLE
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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).
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MATHEMATICA
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Select[Range[1, 10^5, 2], CompositeQ[#] && PowerMod[2, #-1, #] == PowerMod[5, #-1, #] == 1 &] (* Amiram Eldar, Jun 29 2019 *)
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PROG
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(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
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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Serhat Sevki Dincer (sevki(AT)ug.bilkent.edu.tr), May 05 2003
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STATUS
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approved
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