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%I #28 Jun 20 2021 03:11:10
%S 2,3,4,5,7,8,11,13,15,16,17,18,19,21,23,27,29,31,32,33,35,36,37,39,41,
%T 43,45,47,50,51,53,55,57,59,61,63,64,65,67,69,71,72,73,75,77,79,83,85,
%U 87,89,91,93,95,97,98,99,100,101,103,105,107,109,111,113,115,117,119
%N Numbers whose sum of proper divisors is odd.
%C Numbers which are twice squares, even squares or odd nonsquares.
%H Reinhard Zumkeller, <a href="/A053868/b053868.txt">Table of n, a(n) for n = 1..10000</a>
%o (Haskell)
%o a053868 n = a053868_list !! (n-1)
%o a053868_list = filter (odd . a001065) [1..]
%o -- _Reinhard Zumkeller_, Nov 01 2015, Sep 15 2011
%Y Cf. A000203, A001065, A028982, A053869.
%K nonn
%O 1,1
%A _Henry Bottomley_, Mar 29 2000
%E Improved name from _Omar E. Pol_, Aug 14 2009