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A057710 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. 4
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; text; internal format)
OFFSET

1,1

LINKS

T. D. Noe, Table of n, a(n) for n=1..1000

Eric Weisstein's World of Mathematics, Restricted Divisor Function

Eric Weisstein's World of Mathematics, Aliquot sequence.

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).

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, {}] (* Jean-Fran├žois Alcover, Oct 07 2011 *)

CROSSREFS

Cf. A001065, A005114.

Sequence in context: A274001 A324212 A160133 * A285678 A027706 A047336

Adjacent sequences:  A057707 A057708 A057709 * A057711 A057712 A057713

KEYWORD

nonn

AUTHOR

Jack Brennen, Oct 24 2000

STATUS

approved

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Last modified June 24 17:50 EDT 2019. Contains 324330 sequences. (Running on oeis4.)