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A191485
Numbers n=k^2-k+1 such that 2^k == 1 (mod n).
0
1, 3, 7, 73, 601, 8191, 262657, 8640661
OFFSET
1,2
COMMENTS
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.
EXAMPLE
k = 9;
n = k^2 - k + 1 = 81 - 9 + 1 = 73;
2^9 == 1 (mod 73).
PROG
(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 */
CROSSREFS
Sequence in context: A342546 A088647 A075611 * A119572 A362651 A172995
KEYWORD
nonn
AUTHOR
Alzhekeyev Ascar M, Jun 03 2011
STATUS
approved