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 A136804 #22 Nov 17 2017 03:27:16
%S A136804 3,5,6,7,10,12,14,19,20,24,27,28,33,37,38,39,40,41,43,45,47,48,51,53,
%T A136804 54,55,56,63,65,66,69,71,74,75,76,77,78,80,82,83,85,86,87,90,91,93,94,
%U A136804 96,97,101,102,103,105,106,107,108,109,110,112,115,119,125,126
%N A136804 Nonsquares mod 257.
%C A136804 Because 257 is a Fermat prime, these numbers are all primitive roots (mod 257). Complement of A136803.
%H A136804 Nathaniel Johnston, <a href="/A136804/b136804.txt">Table of n, a(n) for n = 1..128</a> (full sequence)
%H A136804 <a href="/index/Sq#squares">Index entries for sequences related to squares</a>
%F A136804 a(n) + a(129-n) = 257.
%p A136804 A136804 := {$(0..256)}: for n from 0 to 256 do A136804 := A136804 minus {n^2 mod 257}: od: op(sort(convert(A136804,list))); # _Nathaniel Johnston_, Jun 23 2011
%t A136804 p=257; Select[Range[0,p-1], JacobiSymbol[ #,p]==-1&]
%o A136804 (PARI) for (n=0, 256, if (! issquare(Mod(n, 257)), print1(n, ", "))) \\ _Michel Marcus_, Mar 12 2017
%o A136804 (PARI) A136804=setminus(S=[0..256],Set([k^2 | k <- S]%257)); \\ _M. F. Hasler_, Nov 15 2017
%Y A136804 Cf. A136803 (squares mod 257), A136805 and A136806 (squares/nonsquares mod 65537).
%K A136804 fini,full,easy,nonn
%O A136804 1,1
%A A136804 _T. D. Noe_, Jan 22 2008