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%I #14 May 19 2019 13:11:32
%S 2,9,19,98,141,176,319,396,467,691,729,970,1113,1279,1447,1473,1873,
%T 1974,2403,3712,5208,5965,6777,7183,8353,8769,8881,8962,10137,10180,
%U 10771,11314,12016,12241,13624,15196,19683,19705,20053,20553,21241
%N Numbers k such that k + sigma(k) + sigma(sigma(k)) is a square.
%H John Cerkan, <a href="/A116014/b116014.txt">Table of n, a(n) for n = 1..10000</a>
%e 1113 + sigma(1113) + sigma(sigma(1113)) = 89^2.
%t okQ[n_]:=Module[{dsn=DivisorSigma[1,n]}, IntegerQ[Sqrt[n+dsn+DivisorSigma[1,dsn]]]]; Select[Range[22000],okQ] (* _Harvey P. Dale_, Jan 23 2011 *)
%o (PARI) is(n)=my(s=sigma(n)); issquare(n+s+sigma(s)) \\ _Charles R Greathouse IV_, Jul 30 2016
%Y Cf. A116012, A116013, A116015.
%K nonn
%O 1,1
%A _Giovanni Resta_, Feb 13 2006