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A015863
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Numbers k such that sigma(k) = sigma(k+4).
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15
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51, 66, 115, 220, 319, 1003, 2585, 4024, 4183, 4195, 5720, 5826, 5959, 8004, 8374, 11659, 12367, 12561, 13581, 14338, 15365, 16116, 17840, 18718, 20541, 25130, 29393, 30170, 32665, 36516, 39913, 40660, 42423, 42922, 47841, 49762
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listen;
history;
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OFFSET
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1,1
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REFERENCES
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J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 51, p. 19, Ellipses, Paris 2008.
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LINKS
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MATHEMATICA
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Select[Range[60000], DivisorSigma[1, #]==DivisorSigma[1, # + 4] &] (* Vincenzo Librandi, Mar 10 2014 *)
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PROG
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CROSSREFS
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Cf. A002961, A007373, A015861, A015865, A015866, A015867, A015876, A015877, A015880, A015881, A015882, A015883, A181647.
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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