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 A371935 #19 Apr 21 2025 11:47:33
%S A371935 9,1,9,3,9,5,3,8,8,2,6,3,7,2,0,5,6,5,1,9,8,1,2,6,7,8,5,1,1,4,0,4,6,7,
%T A371935 9,2,5,3,5,3,7,9,1,5,8,7,6,4,1,5,5,5,4,4,6,5,9,8,0,5,4,8,9,2,3,7,7,9,
%U A371935 9,2,1,0,4,5,1,0,5,6,4,7,0,9,6,4,0,9
%N A371935 Decimal expansion of Sum_{k>=0} (-1)^k / ((k+1)*(2*k+1)!).
%F A371935 Equals 2*(1 - cos(1)) = 2 * A371936.
%F A371935 From _Hugo Pfoertner_, Apr 26 2024: (Start)
%F A371935 Equals A243596/Pi.
%F A371935 Equals A272795^2. (End)
%e A371935 0.91939538826372056519812678511404679253...
%t A371935 s = N[Sum[(-1)^k/((k + 1) (2 k + 1)!), {k, 0, Infinity}], 120]
%t A371935 First[RealDigits[s]]
%o A371935 (PARI) 2*(1 - cos(1)) \\ _Stefano Spezia_, Apr 21 2025
%Y A371935 Cf. A049470, A243596, A272795, A371936.
%K A371935 nonn,cons
%O A371935 0,1
%A A371935 _Clark Kimberling_, Apr 24 2024