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A067465
Numbers k such that sigma(k^2+1) is a perfect square.
1
0, 13, 64, 67, 189, 344, 900, 2499, 3028, 4253, 5257, 6277, 9075, 11516, 12544, 18739, 18925, 47018, 49011, 62355, 72981, 112061, 125011, 125653, 152765, 167820, 168317, 174724, 179040, 225492, 240597, 251568, 261163, 302128, 302812, 345283
OFFSET
1,2
LINKS
MATHEMATICA
Select[Range[0, 400000], IntegerQ[Sqrt[DivisorSigma[1, #^2+1]]]&] (* Harvey P. Dale, May 14 2018 *)
PROG
(PARI) for(n=0, 500000, if(issquare(sigma(n^2+1)), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Feb 23 2002
EXTENSIONS
More terms from Rick L. Shepherd, Apr 16 2002
STATUS
approved