OFFSET
1,2
REFERENCES
Jean-Marie De Koninck, Ces nombres qui nous fascinent, Entry 42, p. 16, Ellipses, Paris, 2008.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..1000 (terms 1..99 from M. F. Hasler, terms 100..500 from Donovan Johnson)
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
KEYWORD
nonn
AUTHOR
STATUS
approved
