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 A155450 #35 Mar 05 2024 11:26:15
%S A155450 5,18,28,41,51,64,74,87,97,110,120,133,143,156,166,179,189,202,212,
%T A155450 225,235,248,258,271,281,294,304,317,327,340,350,363,373,386,396,409,
%U A155450 419,432,442,455,465,478,488,501,511,524,534,547,557,570,580,593,603,616
%N A155450 Numbers congruent to 5 or 18 mod 23.
%C A155450 Or, numbers n such that n^2 == 2 mod 23.
%H A155450 Vincenzo Librandi, <a href="/A155450/b155450.txt">Table of n, a(n) for n = 1..1000</a>
%H A155450 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,1,-1).
%F A155450 a(n) = a(n-1)+a(n-2)-a(n-3), with a(1)=5, a(2)=18, a(3)=28.
%F A155450 G.f.: x*(5 + 13*x + 5*x^2)/((1 + x)*(1 - x)^2). - _Vincenzo Librandi_, May 03 2014
%F A155450 Sum_{n>=1} (-1)^(n+1)/a(n) = cot(5*Pi/23)*Pi/23. - _Amiram Eldar_, Feb 26 2023
%t A155450 LinearRecurrence[{1,1,-1},{5,18,28},80] (* _Vincenzo Librandi_, Feb 29 2012 *)
%t A155450 CoefficientList[Series[(5 + 13 x + 5 x^2)/((1 + x) (1 - x)^2), {x, 0, 60}], x] (* _Vincenzo Librandi_, May 03 2014 *)
%K A155450 nonn,easy
%O A155450 1,1
%A A155450 _Vincenzo Librandi_, Jan 22 2009
%E A155450 New name from _Charles R Greathouse IV_, Jan 11 2012