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A093439
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Least number n with a given prime signature such that all numbers >= n with this prime signature are one less than a composite number.
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1
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3, 8, 9, 32, 64, 81, 128, 216, 512, 1024, 1728, 2048, 4096, 6561, 7776, 8192, 13824, 16384, 27000, 32768, 46656, 110592, 131072, 216000, 248832, 262144, 279936, 373248, 524288, 884736, 1048576, 1728000, 2097152, 2985984, 4194304, 5832000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| This is to categorize prime signatures such that p^a*q^b*r^c ... +1 is composite, p,q,r are arbtrarily chosen primes. example: Prefect odd powers + 1 is always composite. Are there other examples?exceptions like 3 and 5 are to be ignored.
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EXAMPLE
| 8 = 2^3 is a member as 8 has a prime signature p^3 and all numbers of the form p^3+1 are composite.
9 is also a member though 2^2 +1 = 5 is a prime but for all odd primes p^2 +1 is even.
216 = 2^3*3^3 is a member because p^3*q^3+1 is always divisible by pq+1.
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CROSSREFS
| Cf. A093438.
Sequence in context: A167344 A025615 A101720 * A000927 A055513 A038226
Adjacent sequences: A093436 A093437 A093438 * A093440 A093441 A093442
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KEYWORD
| nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Apr 01 2004
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EXTENSIONS
| More terms from David Wasserman (dwasserm(AT)earthlink.net), Sep 12 2006
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