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 A087967 #17 Jul 15 2024 10:23:15 %S A087967 18,36,72,90,100,126,144,147,162,180,198,200,234,252,288,294,300,306, %T A087967 324,342,360,396,400,414,441,450,468,504,522,558,576,588,600,612,630, %U A087967 648,666,684,700,720,735,738,774,792,800,810,828,846,882,900,936,954 %N A087967 Integers m such that gcd(2^m-1, m^2) is not a square number. %H A087967 Amiram Eldar, <a href="/A087967/b087967.txt">Table of n, a(n) for n = 1..10000</a> %e A087967 For m = 18: gcd(262143, 324) = 27 is not a square number, so 18 is a term. %t A087967 Select[Range[1000], !IntegerQ[Sqrt[GCD[2^#-1, #^2]]] &] %o A087967 (PARI) isok(m) = !issquare(gcd(2^m-1, m^2)); \\ _Michel Marcus_, Aug 27 2019 %Y A087967 Cf. A087966, A087969. %K A087967 nonn %O A087967 1,1 %A A087967 _Labos Elemer_, Sep 22 2003