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Search: id:A025475
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| A025475 |
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Prime powers p^m, m = 0 or m >= 2, thus excluding the primes. |
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+0
104
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| 1, 4, 8, 9, 16, 25, 27, 32, 49, 64, 81, 121, 125, 128, 169, 243, 256, 289, 343, 361, 512, 529, 625, 729, 841, 961, 1024, 1331, 1369, 1681, 1849, 2048, 2187, 2197, 2209, 2401, 2809, 3125, 3481, 3721, 4096, 4489, 4913, 5041, 5329, 6241, 6561, 6859, 6889, 7921, 8192
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Also nonprime n such that sigma(n)*phi(n)>(n-1)^2 - Benoit Cloitre (benoit7848c(AT)orange.fr), Apr 12 2002
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..10000
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.
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FORMULA
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A005171(a(n))*A010055(n)) = 1. [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Nov 01 2009]
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MATHEMATICA
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Select[ Range[ 2, 10000 ], ! PrimeQ[ # ] && Mod[ #, # - EulerPhi[ # ] ] == 0 & ]
Sort[ Flatten[ Table[ Prime[n]^i, {n, 1, PrimePi[ Sqrt[10^4]]}, {i, 2, Log[ Prime[n], 10^4]}]]]
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PROGRAM
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(PARI) for(n=1, 10000, if(sigma(n)*eulerphi(n)*(1-isprime(n))>(n-1)^2, print1(n, ", ")))
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CROSSREFS
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Cf. A001597. Differences give A053707.
Sequence in context: A134601 A134611 A134612 this_sequence A125643 A002760 A115651
Adjacent sequences: A025472 A025473 A025474 this_sequence A025476 A025477 A025478
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KEYWORD
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nonn,easy,nice
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AUTHOR
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David W. Wilson (davidwwilson(AT)comcast.net)
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EXTENSIONS
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Edited by Daniel Forgues (squid(AT)zensearch.com), Aug 18 2009
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