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 A070449 #25 Dec 18 2023 13:22:03
%S A070449 0,1,4,9,16,25,9,22,10,0,19,13,9,7,7,9,13,19,0,10,22,9,25,16,9,4,1,0,
%T A070449 1,4,9,16,25,9,22,10,0,19,13,9,7,7,9,13,19,0,10,22,9,25,16,9,4,1,0,1,
%U A070449 4,9,16,25,9,22,10,0,19,13,9,7,7,9,13,19,0,10,22,9,25,16,9,4,1,0,1,4,9,16
%N A070449 a(n) = n^2 mod 27.
%H A070449 G. C. Greubel, <a href="/A070449/b070449.txt">Table of n, a(n) for n = 0..1000</a>
%H A070449 <a href="/index/Rec#order_27">Index entries for linear recurrences with constant coefficients</a>, signature (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1).
%F A070449 a(n) = a(n-27). - _G. C. Greubel_, Mar 24 2016
%F A070449 G.f.:(x + 4*x^2 + 9*x^3 + 16*x^4 + 25*x^5 + 9*x^6 + 22*x^7 + 10*x^8 + 19*x^10 + 13*x^11 + 9*x^12 + 7*x^13 + 7*x^14 + 9*x^15 + 13*x^16 + 19*x^17 + 10*x^19 + 22*x^20 + 9*x^21 + 25*x^22 + 16*x^23 + 9*x^24 + 4*x^25 + x^26)/(1 - x^27). - _Vincenzo Librandi_, Mar 25 2016
%t A070449 Table[Mod[n^2,27],{n,0,200}] (* _Vladimir Joseph Stephan Orlovsky_, Apr 23 2011 *)
%t A070449 PowerMod[Range[0,100],2,27] (* or *) PadRight[{},100,{0,1,4,9,16,25,9,22,10,0,19,13,9,7,7,9,13,19,0,10,22,9,25,16,9,4,1}] (* _Harvey P. Dale_, Dec 17 2023 *)
%o A070449 (PARI) a(n)=n^2%27 \\ _Charles R Greathouse IV_, Apr 06 2016
%K A070449 nonn,easy
%O A070449 0,3
%A A070449 _N. J. A. Sloane_, May 12 2002