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%I #15 Oct 01 2020 03:00:01
%S 5,6,11,12,14,15,19,20,23,24,26,27,28,29,33,34,35,38,39,40,41,42,44,
%T 45,47,53,54,56,57,58,59,60,62,63,65,68,69,74,76,77,78,79,80,82,83,84,
%U 85,86,87,88,89,90,91,92,95,96,99,101,102,103
%N Numbers k such that sigma(k) is a Zumkeller number (A083207).
%C Sequence contains many semiprimes of the form p(m)*p(m+1). Only 6 of the first 200 semiprimes of this form are not terms, those where m is in {15, 37, 99, 100, 121, 197}.
%H Amiram Eldar, <a href="/A337399/b337399.txt">Table of n, a(n) for n = 1..10000</a>
%t zQ[n_]:=Module[{d=Divisors[n],t,ds,x},ds=Plus@@d;If[Mod[ds,2]>0,False,t=CoefficientList[Product[1+x^i,{i,d}],x];t[[1+ds/2]]>0]]; Select[Range[200],zQ[DivisorSigma[1,#]]&] (* code by _T. D. Noe_ at A083207 *)
%Y Cf. A000203, A083207, A320518 (subsequence).
%K nonn,easy
%O 1,1
%A _Ivan N. Ianakiev_, Aug 26 2020