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 A070450 #16 Dec 18 2023 12:37:08
%S A070450 0,1,4,9,16,25,8,21,8,25,16,9,4,1,0,1,4,9,16,25,8,21,8,25,16,9,4,1,0,
%T A070450 1,4,9,16,25,8,21,8,25,16,9,4,1,0,1,4,9,16,25,8,21,8,25,16,9,4,1,0,1,
%U A070450 4,9,16,25,8,21,8,25,16,9,4,1,0,1,4,9,16,25,8,21,8,25,16,9,4,1,0,1,4,9,16
%N A070450 a(n) = n^2 mod 28.
%C A070450 Periodic, with period = 14. - _Harvey P. Dale_, Jul 20 2021
%H A070450 G. C. Greubel, <a href="/A070450/b070450.txt">Table of n, a(n) for n = 0..1000</a>
%H A070450 <a href="/index/Rec#order_14">Index entries for linear recurrences with constant coefficients</a>, signature (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1).
%F A070450 a(n) = a(n-28). - _G. C. Greubel_, Mar 24 2016
%t A070450 Table[Mod[n^2,28],{n,0,200}] (* _Vladimir Joseph Stephan Orlovsky_, Apr 27 2011 *)
%t A070450 PowerMod[Range[0,100],2,28] (* or *) PadRight[{},100,{0,1,4,9,16,25,8,21,8,25,16,9,4,1}] (* _Harvey P. Dale_, Jul 20 2021 *)
%o A070450 (PARI) a(n)=n^2%28 \\ _Charles R Greathouse IV_, Apr 06 2016
%Y A070450 Cf. A070448, A070449.
%K A070450 nonn,easy
%O A070450 0,3
%A A070450 _N. J. A. Sloane_, May 12 2002