A080666 Numbers k such that k^2 + 1 and k^2 - 1 are not squarefree.

7, 41, 43, 57, 82, 93, 99, 107, 117, 118, 143, 157, 168, 193, 207, 239, 243, 251, 257, 293, 307, 327, 332, 343, 357, 368, 393, 407, 437, 443, 457, 493, 507, 515, 532, 540, 543, 557, 568, 577, 593, 606, 607, 643, 657, 693, 707, 743, 746, 757, 775, 776, 782

Offset: 1

Author

Joseph L. Pe, Mar 02 2003

Keywords

• nonn

Comments

This sequence is infinite. For instance, it contains all numbers of the form 100*m + 7. - Emmanuel Vantieghem, Oct 25 2016

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A002522, A005563, A013929.

Programs

Magma

[n : n in [2..800] | not IsSquarefree(n^2-1) and not IsSquarefree(n^2+1)]; // Vincenzo Librandi, Oct 26 2016

Mathematica

Select[Range[10^3], ! SquareFreeQ[ #^2 - 1] && ! SquareFreeQ[ #^2 + 1] &]