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%I #26 Aug 12 2023 04:37:10
%S 1,42,246,287,728,1434,1673,1880,4264,6237,9799,9855,18330,21352,
%T 21385,24856,36531,39990,46655,57270,66815,92664,125255,156570,182665,
%U 208182,212949,242879,273265,380511,391345,411558,539560,627215,693160,730145,741096
%N Numbers whose sum of the squares of divisors is also a square number.
%D Jean-Marie De Koninck, Ces nombres qui nous fascinent, Entry 42, p. 16, Ellipses, Paris, 2008.
%H Amiram Eldar, <a href="/A046655/b046655.txt">Table of n, a(n) for n = 1..1000</a> (terms 1..99 from M. F. Hasler, terms 100..500 from Donovan Johnson)
%H Project Euler, <a href="https://projecteuler.net/problem=211">Problem 211: Divisor Square Sum</a>.
%e 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.
%t Select[Range[750000], IntegerQ[Sqrt[DivisorSigma[2, #]]] &] (* _Jayanta Basu_, Jun 27 2013 *)
%o (PARI) for( n=1,10^6, issquare(sigma(n,2)) && print1(n", ")) \\ _M. F. Hasler_, Oct 05 2008
%Y Cf. A046656, A000290, A001157.
%K nonn
%O 1,2
%A _Labos Elemer_