|
| |
|
|
A025475
|
|
Prime powers p^m, m = 0 or m >= 2, thus excluding the primes.
|
|
108
| |
|
|
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; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,2
|
|
|
COMMENTS
| Also nonprime n such that sigma(n)*phi(n)>(n-1)^2 - Benoit Cloitre, Apr 12 2002
Subsequence of A000961. [Reinhard Zumkeller, Jun 22 2011]
A192280(a(n)) = 0. [Reinhard Zumkeller, Aug 26 2011]
|
|
|
LINKS
| T. D. Noe, Table of n, a(n) for n=1..10000
Eric Weisstein's World of Mathematics, Prime Power
|
|
|
FORMULA
| A005171(a(n))*A010055(a(n)) = 1. [From Reinhard Zumkeller, Nov 01 2009]
|
|
|
MATHEMATICA
| 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]}]]]
|
|
|
PROG
| (PARI) for(n=1, 10000, if(sigma(n)*eulerphi(n)*(1-isprime(n))>(n-1)^2, print1(n, ", ")))
(Haskell)
a025475 n = a025475_list !! (n-1)
a025475_list = filter ((== 0) . a010051) a000961_list
-- Reinhard Zumkeller, Jun 22 2011
(PARI) is_A025475(n)={ ispower(n, , &p) && isprime(p) || n==1 } \\ - M. F. Hasler, Sep 25 2011
|
|
|
CROSSREFS
| Cf. A001597. Differences give A053707.
Cf. A193166.
Sequence in context: A134601 A134611 A134612 * A195942 A125643 A002760
Adjacent sequences: A025472 A025473 A025474 * A025476 A025477 A025478
|
|
|
KEYWORD
| nonn,easy,nice
|
|
|
AUTHOR
| David W. Wilson (davidwwilson(AT)comcast.net)
|
|
|
EXTENSIONS
| Edited by Daniel Forgues (squid(AT)zensearch.com), Aug 18 2009
|
| |
|
|
