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A191485
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Numbers n=k^2-k+1 such that 2^k == 1 (mod n).
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0
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OFFSET
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1,2
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COMMENTS
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The elements of this sequence are elements of the sequence A002061 (Central polygonal numbers).
The first composite number is 8640661 = 31 * 211 * 1321 (31 and 211 are elements of the sequence A002061).
No more terms up to 3773299855577673.
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LINKS
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EXAMPLE
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k = 9;
n = k^2 - k + 1 = 81 - 9 + 1 = 73;
2^9 == 1 (mod 73).
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PROG
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(PARI) for(k=1, 10^9, n=k^2-k+1; if( lift(Mod(2, n)^k)==1, print1(n, ", "))); /* Joerg Arndt, Jun 03 2011 */
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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