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Search: id:A006532
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| A006532 |
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Numbers n such that sum of divisors is a square.
(Formerly M3089)
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+0
16
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| 1, 3, 22, 66, 70, 81, 94, 115, 119, 170, 210, 214, 217, 265, 282, 310, 322, 343, 345, 357, 364, 382, 385, 400, 472, 497, 510, 517, 527, 642, 651, 679, 710, 742, 745, 782, 795, 820, 862, 884, 889, 930, 935, 966, 970, 1004, 1029, 1066, 1080, 1092, 1146
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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If a and b are in the sequence and relatively prime, then a*b is also in the sequence. [From Franklin T. Adams-Watters (FrankTAW(AT)Netscape.net), Jan 12 2009]
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REFERENCES
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A. H. Beiler, Recreations in the Theory of Numbers, Dover, NY, 1964, p. 8.
J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 94, p. 33, Ellipses, Paris 2008.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
D. Wells, Curious and interesting numbers, Penguin Books, p. 111.
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..10000
Index entries for sequences related to sums of squares
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MAPLE
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for i from 1 to 1000 do if issqr(sigma(i)) then print(i); fi; od;
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MATHEMATICA
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Select[ Range[ 1150 ], IntegerQ[ Sqrt[ DivisorSigma[ 1, # ] ] ]& ]
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CROSSREFS
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Cf. A074385, A000203. [From Franklin T. Adams-Watters (FrankTAW(AT)Netscape.net), Jan 12 2009]
Adjacent sequences: A006529 A006530 A006531 this_sequence A006533 A006534 A006535
Sequence in context: A041103 A104604 A139272 this_sequence A005288 A143166 A055550
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KEYWORD
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easy,nonn,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Simon Plouffe (simon.plouffe(AT)gmail.com)
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EXTENSIONS
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Additional reference from Felice Russo (felice.russo(AT)katamail.com). More terms from Enoch Haga (Enokh(AT)comcast.net).
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