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

Author

Giovanni Resta, Feb 06 2006

Keywords

• nonn
• base

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

Examples

			sigma(10231) = 11032, sigma(31812) = 81312.
		

Links

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

Crossrefs

Cf. A000203, A114065, A115921, A175795.

Programs

Mathematica

Select[Range[35000],Sort[IntegerDigits[#]]==Sort[ IntegerDigits[ DivisorSigma[ 1,#]]]&] (* Harvey P. Dale, May 09 2013 *)

PARI

isok(n) = vecsort(digits(n)) == vecsort(digits(sigma(n))); \\ Michel Marcus, Dec 13 2015 and May 27 2018

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