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%I #26 Jul 10 2021 06:54:24
%S 12,18,24,31,32,42,48,54,56,60,72,80,84,90,96,98,104,108,114,120,124,
%T 126,128,132,140,144,152,156,168,180,182,186,192,210,216,224,228,234,
%U 240,248,252,264,270,272,280,288,294,308,312,320,324,336,342,360,372,378,384,390
%N Values k such that sigma(x) = k has more than one solution, sigma = A000203.
%C Numbers k with A054973(k) >= 2. Numbers k which occur in A000203 more than once.
%C Numbers k = A007609(n) with A007609(n+1) - A007609(n) = 0.
%C Does this sequence have finite density? - _Franklin T. Adams-Watters_, Jun 18 2009
%C See A300869 for the odd terms, much less frequent since they can only occur for x = k^2 or 2*k^2. - _M. F. Hasler_, Mar 16 2018
%H Franklin T. Adams-Watters, <a href="/A159886/b159886.txt">Table of n, a(n) for n = 1..1095</a> (terms <= 10000)
%e a(1)=12 as the multiplicity of the value 12 is 2: 12 = sigma(6) = sigma(11).
%o (PARI)
%o na(n) = local(v, s); v=vector(n);for(k=1,n,s=sigma(k);if(s<=n,v[s]++));v
%o la(n) = local(v, r); v=na(n);r=[];for(k=1,n,if(v[k]>1,r=concat(r,[k])));r \\ _Franklin T. Adams-Watters_, Jun 18 2009
%Y Cf. A000203, A054973, A007609, A007368.
%Y Subsequence of A002191.
%Y Odd terms are listed in A300869.
%K nonn
%O 1,1
%A _Jaroslav Krizek_, Apr 25 2009
%E Edited and extended by _R. J. Mathar_, Apr 28 2009
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