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A116004 Numbers k such that k*sigma(k)*sigma(sigma(k)) is a square. 2

%I

%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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Last modified August 15 16:57 EDT 2022. Contains 356148 sequences. (Running on oeis4.)