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 A272359 #23 Jan 28 2019 03:31:16 %S A272359 364,728,1092,1456,1755,1820,2184,2548,2912,3276,3510,3640,4004,4368, %T A272359 4732,5096,5265,5460,5824,6188,6552,6916,7020,7280,7644,8008,8372, %U A272359 8736,8775,9100,9464,9828,10192,10530,10556,10920,11284,11648,12012,12285,12376,12740,13104,13468 %N A272359 Numbers n such that (2^n - 1) / gcd(n, 2^n - 1) is not squarefree. %C A272359 Multiples of A002326((q-1)/2), where q is a Wieferich prime A001220. %H A272359 Charles R Greathouse IV, <a href="/A272359/b272359.txt">Table of n, a(n) for n = 1..10000</a> %o A272359 (PARI) isok(n) = my(m=2^n-1); !issquarefree(m/gcd(n, m)); \\ _Michel Marcus_, Apr 27 2016 %Y A272359 Cf. A049094, A272361. %K A272359 nonn %O A272359 1,1 %A A272359 _Thomas Ordowski_, Apr 27 2016