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 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 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

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Last modified May 21 09:41 EDT 2024. Contains 372733 sequences. (Running on oeis4.)