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

1,1

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

Mathematica

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

Prog

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

Crossrefs

Cf. A002522, A005563, A013929.

Sequence in context: A144421 A023251 A073501 * A224718 A374234 A272387

Adjacent sequences: A080663 A080664 A080665 * A080667 A080668 A080669

Keyword

nonn

Author

Joseph L. Pe, Mar 02 2003

Status

approved