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A015866 Numbers k such that sigma(k) = sigma(k+6). 15
20, 155, 182, 184, 203, 264, 621, 650, 702, 852, 893, 944, 1343, 1357, 2024, 2544, 2990, 4130, 4183, 4450, 5428, 5835, 6149, 6313, 6572, 8177, 8695, 11208, 11333, 11991, 12444, 12561, 12859, 13595, 14857, 16815, 18203, 18330, 18430, 19089 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Up to 10^13, sigma(k-6) = sigma(k) = sigma(k+6) only for k = 33227, 604453 and 4223105512993. - Giovanni Resta, Mar 03 2014
REFERENCES
J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 20, pp 7, Ellipses, Paris 2008.
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..10000 (first 1000 terms from Donovan Johnson)
A. Weingartner, On the Solutions of sigma(n) = sigma(n+k), Journal of Integer Sequences, Vol. 14 (2011), #11.5.5.
MATHEMATICA
Select[Range[20000], DivisorSigma[1, #]==DivisorSigma[1, # + 6] &] (* Vincenzo Librandi, Mar 10 2014 *)
PROG
(PARI) is(n)=sigma(n)==sigma(n+6) \\ Charles R Greathouse IV, Mar 09 2014
CROSSREFS
Sequence in context: A108647 A164605 A000492 * A101091 A120693 A120692
KEYWORD
nonn
AUTHOR
STATUS
approved

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Last modified March 28 16:28 EDT 2024. Contains 371254 sequences. (Running on oeis4.)