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 A272475 #14 Sep 08 2022 08:46:16 %S A272475 4,6,8,10,11,12,16,18,20,22,23,24,28,30,32,33,35,36,40,42,43,44,46,48, %T A272475 50,52,54,55,56,58,60,64,66,68,69,70,72,75,76,77,78,80,82,83,84,86,88, %U A272475 90,92,95,96,99,100,102,104,105,106,108,110,112,114,115,116,117 %N A272475 Numbers n such that 2^n-1 and 3^n-1 are not coprime. %C A272475 Complement of A263647. %H A272475 Vincenzo Librandi, <a href="/A272475/b272475.txt">Table of n, a(n) for n = 1..1000</a> %e A272475 gcd(2^4-1, 3^4-1) = gcd(15,80) = 5, so a(1) = 4. %t A272475 Select[Range[200], ! GCD[2^# - 1, 3^# - 1] == 1 &] %o A272475 (Magma) [n: n in [1..200] | not Gcd(2^n-1, 3^n-1) eq 1]; %o A272475 (PARI) isok(n) = gcd(2^n-1, 3^n-1) != 1; \\ _Michel Marcus_, May 01 2016 %Y A272475 Cf. A263647. %K A272475 nonn %O A272475 1,1 %A A272475 _Vincenzo Librandi_, May 01 2016