This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A080666 #27 Sep 08 2022 08:45:09 %S A080666 7,41,43,57,82,93,99,107,117,118,143,157,168,193,207,239,243,251,257, %T A080666 293,307,327,332,343,357,368,393,407,437,443,457,493,507,515,532,540, %U A080666 543,557,568,577,593,606,607,643,657,693,707,743,746,757,775,776,782 %N A080666 Numbers k such that k^2 + 1 and k^2 - 1 are not squarefree. %C A080666 This sequence is infinite. For instance, it contains all numbers of the form 100*m + 7. - _Emmanuel Vantieghem_, Oct 25 2016 %H A080666 Amiram Eldar, <a href="/A080666/b080666.txt">Table of n, a(n) for n = 1..10000</a> %t A080666 Select[Range[10^3], ! SquareFreeQ[ #^2 - 1] && ! SquareFreeQ[ #^2 + 1] &] %o A080666 (Magma) [n : n in [2..800] | not IsSquarefree(n^2-1) and not IsSquarefree(n^2+1)]; // _Vincenzo Librandi_, Oct 26 2016 %Y A080666 Cf. A002522, A005563, A013929. %K A080666 nonn %O A080666 1,1 %A A080666 _Joseph L. Pe_, Mar 02 2003