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A375917
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Composite numbers k == 1, 11 (mod 12) such that 3^((k-1)/2) == 1 (mod k).
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0
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121, 1729, 2821, 7381, 8401, 10585, 15457, 15841, 18721, 19345, 23521, 24661, 28009, 29341, 31621, 41041, 46657, 47197, 49141, 50881, 52633, 55969, 63973, 74593, 75361, 82513, 87913, 88573, 93961, 111361, 112141, 115921, 125665, 126217, 138481, 148417, 172081
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OFFSET
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1,1
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COMMENTS
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Odd composite numbers k such that 3^((k-1)/2) == (3/k) = 1 (mod k), where (3/k) is the Jacobi symbol (or Kronecker symbol).
It seems that most terms are congruent to 1 modulo 12. The first terms congruent to 11 modulo 12 are 1683683, 1898999, 2586083, 2795519, 4042403, 4099439, 5087171, 8243111, ...
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LINKS
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EXAMPLE
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1683683 is a term because 1683683 = 59*28537 is composite, 1683683 == 11 (mod 12), and 3^((1683683-1)/2) == 1 (mod 1683683).
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PROG
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(PARI) isA375917(k) = (k>1) && !isprime(k) && (k%12==1 || k%12==11) && Mod(3, k)^((k-1)/2) == 1
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CROSSREFS
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| b=2 | b=3 | b=5 |
-----------------------------------+-------------------+----------+---------+
-----------------------------------+-------------------+----------+---------+
-----------------------------------+-------------------+----------+---------+
b^((k-1)/2)==-(b/k) (mod k), | | | |
(b/k)=-1, b^((k-1)/2)==1 (mod k) | | | |
-----------------------------------+-------------------+----------+---------+
(union of first two) | | | |
-----------------------------------+-------------------+----------+---------+
(union of all three) | | | |
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KEYWORD
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nonn,new
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AUTHOR
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STATUS
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approved
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