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A057710
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Positive integers n with exactly 2 aliquot sequence predecessors. In other words, there are exactly two solutions x for which s(x)=n. The function s(x) here refers to the Restricted Divisor Function, the sum of all proper divisors of x.
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4
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6, 8, 13, 14, 15, 16, 17, 19, 20, 22, 23, 27, 29, 32, 42, 44, 46, 50, 54, 62, 69, 90, 92, 100, 104, 108, 110, 114, 130, 136, 148, 150, 152, 156, 166, 170, 176, 182, 184, 186, 198, 200, 202, 214, 230, 232, 234, 236, 240, 242, 244, 254, 258, 266, 272, 280, 286
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..1000
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics (1).
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics (2).
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EXAMPLE
| 14 is a member of the sequence because s(22)=14 and s(169)=14 (and because no other integer x satisfies s(x)=14).
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MATHEMATICA
| len = max = 57; f[_List] := (s = Select[ Split[ Sort[ Table[ DivisorSigma[1, n] - n, {n, 1, max *= 2}]]], Length[#] == 2 & ][[All, 1]]; s [[1 ;; Min[len, Length[s]]]]); FixedPoint[f, {}] (* From Jean-François Alcover, Oct 07 2011 *)
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CROSSREFS
| Cf. A001065, A005114.
Sequence in context: A077670 A072057 A160133 * A027706 A047336 A181449
Adjacent sequences: A057707 A057708 A057709 * A057711 A057712 A057713
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KEYWORD
| nonn
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AUTHOR
| Jack Brennen (jb(AT)brennen.net), Oct 24 2000
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