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 A028794 #9 Dec 27 2019 16:21:17 %S A028794 2,3,5,6,8,11,12,14,15,17,18,20,21,23,24,26,27,29,30,32,33,35,38,39, %T A028794 41,42,44,45,47,48,50,51,53,54,56,57,59,60,62,65,66,68,69,71,72,74,75, %U A028794 77,78,80 %N A028794 Nonsquares mod 81. %t A028794 Complement[Range[0, 80], PowerMod[Range[81], 2, 81]] (* _Alonso del Arte_, Dec 27 2019 *) %o A028794 (Scala) (0 to 80).diff((1 to 81).map(n => (n * n) % 81)) // _Alonso del Arte_, Dec 27 2019 %Y A028794 Cf. A010442. %K A028794 nonn,fini,full,easy %O A028794 1,1 %A A028794 _N. J. A. Sloane_