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%I #12 Oct 02 2017 10:55:05
%S 6,22,33,44,69,76,82,140,190,295,354,392,423,451,531,581,650,944,1072,
%T 1119,1142,1150,1668,2276,2893,4043,4163,4176,4192,4257,4262,4509,
%U 5090,5975,7260,8660,12977,14927,15026,15753,16064,19105
%N Composite n such that phi(n) * sigma(n) is one less than a square.
%H Donovan Johnson, <a href="/A015709/b015709.txt">Table of n, a(n) for n = 1..500</a>
%H Richard K. Guy, <a href="http://www.jstor.org/stable/2974586">Divisors and desires</a>, Amer. Math. Monthly, 104 (1997), 359-360.
%o (PARI) isok(n) = !isprime(n) && issquare(eulerphi(n)*sigma(n)+1); \\ _Michel Marcus_, Oct 02 2017
%K nonn
%O 1,1
%A _Robert G. Wilson v_
%E Offset corrected by _Donovan Johnson_, Apr 02 2012
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