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 A308573 #27 Jun 11 2019 07:09:43
%S A308573 2,1,6,3,5,1,4,6,7,6,0,0,3,2,5,7,8,4,2,4,2,9,5,8,1,5,3,7,4,7,2,4,8,3,
%T A308573 0,7,5,3,3,9,8,8,9,4,6,7,9,3,6,1,7,3,8,8,2,9,3,9,4,9,4,1,7,7,7,4,6,0,
%U A308573 1,9,9,5,3,9,2,9,5,7,0,8,0,5,2,2,1,2,9,9,9,2,7,5,5,1,7,9,9,2,0,9,5,5,7,7,9,3,1,9,9,8,1,5,8,2,9,2,1,1,7,0
%N A308573 Decimal expansion of convergent series Sum_{n >= 1} (cos(n)/2)^n.
%e A308573 0.2163514676003257842429581537472483...
%o A308573 (PARI) suminf(n = 1, (cos(n) / 2)^n) \\ _Michel Marcus_, Jun 08 2019
%K A308573 nonn,cons
%O A308573 0,1
%A A308573 _Neven Sajko_, Jun 08 2019