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 A228141 #26 Jun 22 2025 17:35:53
%S A228141 1,5,21,25,41,45,61,65,81,85,101,105,121,125,141,145,161,165,181,185,
%T A228141 201,205,221,225,241,245,261,265,281,285,301,305,321,325,341,345,361,
%U A228141 365,381,385,401,405,421,425,441,445,461,465,481,485,501,505,521,525
%N A228141 Numbers that are congruent to {1, 5} mod 20.
%H A228141 Colin Barker, <a href="/A228141/b228141.txt">Table of n, a(n) for n = 1..1000</a>
%H A228141 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,1,-1).
%F A228141 a(n) = -3*(4+(-1)^n) + 10*n.
%F A228141 a(n) = a(n-1) + a(n-2) - a(n-3).
%F A228141 G.f.: x*(15*x^2+4*x+1) / ((x-1)^2*(x+1)).
%F A228141 E.g.f.: 15 + (10*x - 12)*exp(x) - 3*exp(-x). - _David Lovler_, Sep 05 2022
%t A228141 Flatten[Table[20n + {1, 5}, {n, 0, 24}]] (* _Alonso del Arte_, Aug 12 2013 *)
%o A228141 (PARI) Vec(x*(15*x^2+4*x+1)/((x-1)^2*(x+1)) + O(x^100))
%Y A228141 Cf. A216815, A122870, A228142.
%K A228141 nonn,easy
%O A228141 1,2
%A A228141 _Colin Barker_, Aug 12 2013