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A116004 Numbers n such that n*sigma(n)*sigma(sigma(n)) is a square. 2
1, 42, 234, 2430, 3510, 3724, 6750, 49005, 72618, 165726, 167580, 318091, 412776, 510489, 642096, 771875, 816998, 859740, 1003275, 1073452, 1166719, 1368576, 1604645, 1712256, 1984500, 2297762, 2500875, 2735810, 2852928, 3082950, 3447360, 4218480, 4258704 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..100

EXAMPLE

234*sigma(234)*sigma(sigma(234))=13104^2.

PROG

(PARI) isok(n) = issquare(n*sigma(n)*sigma(sigma(n))); \\ Michel Marcus, Jan 27 2014

CROSSREFS

Cf. A116005.

Sequence in context: A154472 A221523 A263304 * A221426 A122242 A046655

Adjacent sequences:  A116001 A116002 A116003 * A116005 A116006 A116007

KEYWORD

nonn

AUTHOR

Giovanni Resta, Feb 13 2006

STATUS

approved

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Last modified August 20 18:11 EDT 2019. Contains 326154 sequences. (Running on oeis4.)