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 A028743 #10 Nov 30 2019 16:46:13 %S A028743 2,3,5,7,8,11,12,13,14,17,18,20,22,23,26,27,28,29 %N A028743 Nonsquares mod 30. %e A028743 Since 5 is not a perfect square and there are no solutions to x^2 = 5 mod 30, 5 is in the sequence. %e A028743 Although 6 is not a perfect square either, there are solutions to x^2 = 6 mod 30, such as x = 6, x = 24, so 6 is not in the sequence. %t A028743 Complement[Range[30], PowerMod[Range[30], 2, 30]] (* _Alonso del Arte_, Nov 30 2019 *) %o A028743 (Scala) val squaresMod30 = (1 to 30).map(n => n * n).map(_ % 30) %o A028743 (0 to 29).diff(squaresMod30) // _Alonso del Arte_, Nov 30 2019 %Y A028743 Cf. A010462. %K A028743 nonn,fini,full %O A028743 1,1 %A A028743 _N. J. A. Sloane_ %E A028743 Incorrect term 15 removed by _Alonso del Arte_, Nov 30 2019