Search: id:A025475
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%I A025475
%S A025475 1,4,8,9,16,25,27,32,49,64,81,121,125,128,169,243,256,289,343,361,512,
               529,
%T A025475 625,729,841,961,1024,1331,1369,1681,1849,2048,2187,2197,2209,2401,2809,
%U A025475 3125,3481,3721,4096,4489,4913,5041,5329,6241,6561,6859,6889,7921,8192
%N A025475 Prime powers p^m, m = 0 or m >= 2, thus excluding the primes.
%C A025475 Also nonprime n such that sigma(n)*phi(n)>(n-1)^2 - Benoit Cloitre (benoit7848c(AT)orange.fr), 
               Apr 12 2002
%H A025475 T. D. Noe, <a href="b025475.txt">Table of n, a(n) for n=1..10000</a>
%H A025475 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               PrimePower.html">Link to a section of The World of Mathematics.</
               a>
%F A025475 A005171(a(n))*A010055(n)) = 1. [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), 
               Nov 01 2009]
%t A025475 Select[ Range[ 2, 10000 ], ! PrimeQ[ # ] && Mod[ #, # - EulerPhi[ # ] 
               ] == 0 & ]
%t A025475 Sort[ Flatten[ Table[ Prime[n]^i, {n, 1, PrimePi[ Sqrt[10^4]]}, {i, 2, 
               Log[ Prime[n], 10^4]}]]]
%o A025475 (PARI) for(n=1,10000,if(sigma(n)*eulerphi(n)*(1-isprime(n))>(n-1)^2,print1(n,
               ",")))
%Y A025475 Cf. A001597. Differences give A053707.
%Y A025475 Sequence in context: A134601 A134611 A134612 this_sequence A125643 A002760 
               A115651
%Y A025475 Adjacent sequences: A025472 A025473 A025474 this_sequence A025476 A025477 
               A025478
%K A025475 nonn,easy,nice
%O A025475 1,2
%A A025475 David W. Wilson (davidwwilson(AT)comcast.net)
%E A025475 Edited by Daniel Forgues (squid(AT)zensearch.com), Aug 18 2009

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