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A046655 Sum of the squares of divisors is also a square number. 3
1, 42, 246, 287, 728, 1434, 1673, 1880, 4264, 6237, 9799, 9855, 18330, 21352, 21385, 24856, 36531, 39990, 46655, 57270, 66815, 92664, 125255, 156570, 182665, 208182, 212949, 242879, 273265, 380511, 391345, 411558, 539560, 627215, 693160, 730145, 741096 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 42, p. 16, Ellipses, Paris 2008.

LINKS

M. F. Hasler and Donovan Johnson, Table of n, a(n) for n = 1..500 (first 99 terms from M. F. Hasler)

Project Euler, Problem 211: Divisor Square Sum.

EXAMPLE

a(3) = 246 = 2*3*41 with 8 divisors: 1,2,3,6,41,82,123,246. The sum of squares of the divisors is 84100 = 290^2, also a square.

MATHEMATICA

Select[Range[750000], IntegerQ[Sqrt[DivisorSigma[2, #]]] &] (* Jayanta Basu, Jun 27 2013 *)

PROG

(PARI) for( n=1, 10^6, issquare(sigma(n, 2)) && print1(n", ")) \\ M. F. Hasler, Oct 05 2008

CROSSREFS

Cf. A046656, A000290, A001157.

Sequence in context: A116004 A221426 A122242 * A156357 A064369 A234043

Adjacent sequences:  A046652 A046653 A046654 * A046656 A046657 A046658

KEYWORD

nonn

AUTHOR

Labos Elemer

STATUS

approved

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Last modified August 21 17:55 EDT 2017. Contains 290893 sequences.