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A137210 Numbers n such that abundance(n) = abundance(sigma(n)). 0
1, 84, 252, 12717, 177744, 189264, 143747328 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..7.

EXAMPLE

abundance(84) = sigma(84) - 2(84) = 56 = abundance(224) = abundance(sigma(84)), so 84 is a term in the sequence.

MATHEMATICA

abund[n_] := DivisorSigma[1, n]-2n; l = {}; For[i = 1, i <= 10^6, i++, If[abund[i] == abund[DivisorSigma[1, i]], l = Append[l, i]]]; l

CROSSREFS

Sequence in context: A112066 A096383 A220043 * A220009 A160321 A249969

Adjacent sequences:  A137207 A137208 A137209 * A137211 A137212 A137213

KEYWORD

nonn

AUTHOR

Joseph L. Pe, Mar 05 2008

EXTENSIONS

a(7) from Donovan Johnson, Apr 27 2008

STATUS

approved

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Last modified September 19 11:16 EDT 2021. Contains 347556 sequences. (Running on oeis4.)