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A115921 Numbers k such that the decimal digits of phi(k) are a permutation of those of k. 14
1, 21, 63, 291, 502, 2518, 2817, 2991, 4435, 5229, 5367, 5637, 6102, 6174, 6543, 6822, 7236, 7422, 8022, 8541, 8982, 17631, 18231, 18261, 20301, 20518, 20617, 21058, 22471, 22851, 25196, 25918, 27615, 29817, 34816, 35683, 43218, 44305 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Contains A069215 and A113781; is itself a subsequence of A082060. - M. F. Hasler, Nov 28 2007
There is some m > 1 such that a(n) > m*n for all n > 1. This follows from the positive density of numbers n such that n/phi(n) > 10. - Charles R Greathouse IV, Sep 07 2012
LINKS
EXAMPLE
phi(20301) = 13200, phi(6543) = 4356.
MATHEMATICA
Select[Range[45000], Sort[IntegerDigits[EulerPhi[#]]]==Sort[IntegerDigits[#]]&] (* Harvey P. Dale, Jul 25 2018 *)
PROG
(PARI) for(n=1, 10^5, if(vecsort(Vecsmall(Str(n)))==vecsort(Vecsmall(Str(eulerphi(n)))), print1(n", "))) \\ M. F. Hasler, Nov 28 2007
(Python)
from sympy import totient
A115921_list = [n for n in range(1, 10**4) if sorted(str(totient(n))) == sorted(str(n))] # Chai Wah Wu, Dec 13 2015
CROSSREFS
Sequence in context: A170930 A113622 A069215 * A251808 A072395 A113781
KEYWORD
nonn,base
AUTHOR
Giovanni Resta, Feb 06 2006
EXTENSIONS
Edited by M. F. Hasler, Nov 28 2007
STATUS
approved

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Last modified March 28 14:02 EDT 2024. Contains 371254 sequences. (Running on oeis4.)