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 A156718 #34 Feb 26 2023 02:34:11
%S A156718 70,99,239,268,408,437,577,606,746,775,915,944,1084,1113,1253,1282,
%T A156718 1422,1451,1591,1620,1760,1789,1929,1958,2098,2127,2267,2296,2436,
%U A156718 2465,2605,2634,2774,2803,2943,2972,3112,3141,3281,3310,3450,3479,3619,3648,3788
%N A156718 Numbers k such that k^2 == -1 (mod 13^2).
%C A156718 Also, numbers of the form 169k +- 70.
%H A156718 Vincenzo Librandi, <a href="/A156718/b156718.txt">Table of n, a(n) for n = 1..10000</a>
%H A156718 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,1,-1).
%F A156718 a(n) = a(n-1) + a(n-2) - a(n-3).
%F A156718 G.f.: x*(70 + 29*x + 70*x^2) / ( (1+x)*(x-1)^2 ). - _Alexander R. Povolotsky_, Feb 15 2009
%F A156718 Sum_{n>=1} (-1)^(n+1)/a(n) = tan(29*Pi/338)*Pi/169. - _Amiram Eldar_, Feb 26 2023
%t A156718 LinearRecurrence[{1,1,-1},{70,99,239},50]
%o A156718 (Magma) [Floor(n/2)*169-70*(-1)^n: n in [1..50]];
%o A156718 (PARI) a(n)=n\2*169-70*(-1)^n \\ _Charles R Greathouse IV_, Dec 23 2011
%Y A156718 Cf. A156636, A156640, A156627, A156639.
%K A156718 nonn,easy
%O A156718 1,1
%A A156718 _Vincenzo Librandi_, Feb 14 2009