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A015866 Numbers n such that sigma(n) = sigma(n + 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(n-6) = sigma(n) = sigma(n+6) only for n = 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

Donovan Johnson and 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.

MAPLE

A015866:=proc(q) local n;

for n from 1 to q do if sigma(n+6)=sigma(n) then print(n); fi; od; end:

A015866(10^10); # Paolo P. Lava, Mar 25 2013

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

Cf. A002961, A007373, A015861, A015863, A015865, A015867, A015876, A015877, A015880, A015881, A015882, A015883, A181647.

Sequence in context: A108647 A164605 A000492 * A101091 A120693 A120692

Adjacent sequences:  A015863 A015864 A015865 * A015867 A015868 A015869

KEYWORD

nonn

AUTHOR

Robert G. Wilson v

STATUS

approved

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Last modified April 9 14:04 EDT 2020. Contains 333353 sequences. (Running on oeis4.)