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%I #12 Jul 15 2021 06:33:54
%S 1,42,234,2430,3510,3724,6750,49005,72618,165726,167580,318091,412776,
%T 510489,642096,771875,816998,859740,1003275,1073452,1166719,1368576,
%U 1604645,1712256,1984500,2297762,2500875,2735810,2852928,3082950,3447360,4218480,4258704
%N Numbers k such that k*sigma(k)*sigma(sigma(k)) is a square.
%H Donovan Johnson, <a href="/A116004/b116004.txt">Table of n, a(n) for n = 1..100</a>
%e 234*sigma(234)*sigma(sigma(234)) = 13104^2.
%o (PARI) isok(n) = issquare(n*sigma(n)*sigma(sigma(n))); \\ _Michel Marcus_, Jan 27 2014
%Y Cf. A116005.
%K nonn
%O 1,2
%A _Giovanni Resta_, Feb 13 2006
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