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A122785
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Nonprimes n such that 8^n==8 (mod n).
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1
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1, 4, 8, 9, 14, 21, 28, 341, 481, 511, 561, 585, 645, 651, 861, 949, 1001, 1016, 1105, 1106, 1281, 1288, 1365, 1387, 1417, 1541, 1649, 1661, 1729, 1736, 1785, 1905, 2044, 2047, 2169, 2465, 2501, 2696, 2701, 2821, 3145, 3171, 3201, 3277, 3605, 3641, 4005
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Theorem: If both numbers q and 2q-1 are primes and n=q*(2q-1) then 8^n==8 (mod n) (n is in the sequence) iff q is of the form 4k+1. 2701,18721,49141,104653,226801,665281,721801,... are such terms.
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MATHEMATICA
| Select[Range[6000], ! PrimeQ[ # ] && Mod[8^#, # ] == Mod[8, # ] &]
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CROSSREFS
| Cf. A020137, A001567.
Sequence in context: A121763 A110087 A085711 * A137055 A078177 A023886
Adjacent sequences: A122782 A122783 A122784 * A122786 A122787 A122788
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KEYWORD
| nonn
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AUTHOR
| Farideh Firoozbakht (mymontain(AT)yahoo.com), Sep 12 2006
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