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A069070
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Numbers n such that n*sigma(n) is a perfect square.
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0
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1, 40, 81, 135, 216, 224, 400, 819, 1372, 3240, 3744, 4650, 6318, 18144, 21700, 27930, 30240, 32400, 32760, 69312, 71148, 91694, 111132, 174592, 175500, 185220, 215472, 241395, 278318, 293907, 327600, 336675, 362700, 386232, 515450, 958737
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Also n such that the squarefree part of n equals the squarefree part of sigma(n)
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PROG
| (PARI) for(n=1, 1000000, if(issquare(n*sigma(n)), print1(n, ", ")))
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CROSSREFS
| Sequence in context: A037975 A039468 A181458 * A174052 A141528 A160282
Adjacent sequences: A069067 A069068 A069069 * A069071 A069072 A069073
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KEYWORD
| easy,nonn
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AUTHOR
| Benoit Cloitre (benoit7848c(AT)orange.fr), Apr 05 2002
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EXTENSIONS
| More terms from Rick L. Shepherd (rshepherd2(AT)hotmail.com), Apr 07 2002
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