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 A113803 #25 Nov 27 2024 07:26:18
%S A113803 3,11,17,25,31,39,45,53,59,67,73,81,87,95,101,109,115,123,129,137,143,
%T A113803 151,157,165,171,179,185,193,199,207,213,221,227,235,241,249,255,263,
%U A113803 269,277,283,291,297,305,311,319,325,333,339,347,353,361,367
%N A113803 Numbers that are congruent to {3, 11} mod 14.
%F A113803 a(n) = 14*n - a(n-1) - 14 (with a(1) = 3). - _Vincenzo Librandi_, Nov 13 2010
%F A113803 From _Wolfdieter Lang_, Dec 15 2011: (Start)
%F A113803 a(n) = 7*n-(7-(-1)^n)/2.
%F A113803 O.g.f.: x*(3+8*x+3*x^2)/((1+x)*(1-x)^2).
%F A113803 See the _Bruno Berselli_ contribution under A113801. (End)
%F A113803 Sum_{n>=1} (-1)^(n+1)/a(n) = cot(3*Pi/14)*Pi/14. - _Amiram Eldar_, Dec 30 2021
%F A113803 From _Amiram Eldar_, Nov 25 2024: (Start)
%F A113803 Product_{n>=1} (1 - (-1)^n/a(n)) = cot(3*Pi/14).
%F A113803 Product_{n>=1} (1 + (-1)^n/a(n)) = sin(Pi/7)*cosec(3*Pi/14). (End)
%t A113803 {3+#,11+#}&/@(14*Range[0,30])//Flatten (* _Harvey P. Dale_, Jun 28 2020 *)
%Y A113803 Third row A113807.
%Y A113803 Cf. A008589, A113801, A113802, A113804, A113805, A113806.
%K A113803 nonn,easy
%O A113803 1,1
%A A113803 _Giovanni Teofilatto_, Jan 22 2006