A067465 Numbers k such that sigma(k^2+1) is a perfect square.

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

Author

Benoit Cloitre, Feb 23 2002

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..300

Crossrefs

Cf. A000203, A000290, A002522, A006532, A193433.

Programs

Mathematica

Select[Range[0,400000],IntegerQ[Sqrt[DivisorSigma[1,#^2+1]]]&] (* Harvey P. Dale, May 14 2018 *)

PARI

for(n=0,500000,if(issquare(sigma(n^2+1)),print1(n,",")))

Extensions

More terms from Rick L. Shepherd, Apr 16 2002