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A006532 Numbers n such that sum of divisors is a square.
(Formerly M3089)
+0
15
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)
OFFSET

1,2

REFERENCES

A. H. Beiler, Recreations in the Theory of Numbers, Dover, NY, 1964, p. 8.

D. Wells, Curious and interesting numbers, Penguin Books, p. 111.

J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 94, p. 33, Ellipses, Paris 2008.

LINKS

T. D. Noe, Table of n, a(n) for n=1..10000

Index entries for sequences related to sums of squares

MAPLE

for i from 1 to 1000 do if issqr(sigma(i)) then print(i); fi; od;

MATHEMATICA

Select[ Range[ 1150 ], IntegerQ[ Sqrt[ DivisorSigma[ 1, # ] ] ]& ]

CROSSREFS

Sequence in context: A041103 A104604 A139272 this_sequence A005288 A055550 A075204

Adjacent sequences: A006529 A006530 A006531 this_sequence A006533 A006534 A006535

KEYWORD

easy,nonn,nice

AUTHOR

njas, Simon Plouffe (plouffe(AT)math.uqam.ca)

EXTENSIONS

Additional reference from Felice Russo (felice.russo(AT)katamail.com). More terms from Enoch Haga (Enokh(AT)comcast.net).

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Last modified September 5 01:44 EDT 2008. Contains 143476 sequences.


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