A115920 Numbers k such that the digits of sigma(k) are a permutation of those of k, in base 10.

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

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

V. Raman, Table of n, a(n) for n = 1..10000

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

Cf. A000203, A114065, A115921, A175795.

Sequence in context: A249899 A009434 A228671 * A183447 A296126 A188546

Adjacent sequences: A115917 A115918 A115919 * A115921 A115922 A115923

Keyword

nonn,base

Author

Giovanni Resta, Feb 06 2006

Status

approved