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Search: id:A020137
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| A020137 |
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Pseudoprimes to base 8. |
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+0
4
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| 9, 21, 45, 63, 65, 105, 117, 133, 153, 231, 273, 341, 481, 511, 561, 585, 645, 651, 861, 949, 1001, 1105, 1281, 1365, 1387, 1417, 1541, 1649, 1661, 1729, 1785, 1905, 2047, 2169, 2465, 2501, 2701, 2821, 3145, 3171, 3201, 3277, 3605, 3641, 4005, 4033, 4097
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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This sequence is a subsequence of the sequence A122785. In fact the terms are odd composite terms of A122785. Theorem: If both numbers q & 2q-1 are primes (q is in the sequence A005382) and n=q*(2q-1) then 8^(n-1)==1 (mod n) (n is in the sequence) iff q is of the form 12k+1. 2701,18721,49141,104653,226801,665281,721801,... is the related subsequence. This subsequence is also a subsequence of the sequence A122785. - Farideh Firoozbakht (mymontain(AT)yahoo.com), Sep 15 2006
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LINKS
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R. J. Mathar, Table of n, a(n) for n=1..613
Index entries for sequences related to pseudoprimes
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MATHEMATICA
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Select[Range[4100], ! PrimeQ[ # ] && PowerMod[8, (# - 1), # ] == 1 &] - Farideh Firoozbakht (mymontain(AT)yahoo.com), Sep 15 2006
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CROSSREFS
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Cf. A005382, A122783, A122785.
Sequence in context: A110680 A163205 A154862 this_sequence A020190 A135187 A133762
Adjacent sequences: A020134 A020135 A020136 this_sequence A020138 A020139 A020140
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KEYWORD
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nonn
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AUTHOR
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David W. Wilson (davidwwilson(AT)comcast.net)
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