|
|
A115920
|
|
Numbers k such that the digits of sigma(k) are a permutation of those of k, in base 10.
|
|
14
|
|
|
1, 69, 258, 270, 276, 609, 639, 2391, 2556, 2931, 3409, 3678, 3679, 4291, 5092, 6937, 8251, 10231, 12087, 12931, 15480, 16387, 20850, 22644, 22893, 24369, 26145, 26442, 27846, 28764, 29880, 29958, 30823, 31812, 32658, 34207, 34758
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
There is some m > 1 such that a(n) > m*n for all n > 1. This follows from the positive density of numbers k such that sigma(k)/k > 10. - Charles R Greathouse IV, Sep 07 2012
|
|
LINKS
|
|
|
EXAMPLE
|
sigma(10231) = 11032, sigma(31812) = 81312.
|
|
MATHEMATICA
|
Select[Range[35000], Sort[IntegerDigits[#]]==Sort[ IntegerDigits[ DivisorSigma[ 1, #]]]&] (* Harvey P. Dale, May 09 2013 *)
|
|
PROG
|
(Python)
from sympy import divisor_sigma
A115920_list = [n for n in range(1, 10**4) if sorted(str(divisor_sigma(n))) == sorted(str(n))] # Chai Wah Wu, Dec 13 2015
(PARI) isok(n) = vecsort(digits(n)) == vecsort(digits(sigma(n))); \\ Michel Marcus, Dec 13 2015 and May 27 2018
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,base
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|