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 A371936 #16 Apr 21 2025 11:47:37
%S A371936 4,5,9,6,9,7,6,9,4,1,3,1,8,6,0,2,8,2,5,9,9,0,6,3,3,9,2,5,5,7,0,2,3,3,
%T A371936 9,6,2,6,7,6,8,9,5,7,9,3,8,2,0,7,7,7,7,2,3,2,9,9,0,2,7,4,4,6,1,8,8,9,
%U A371936 9,6,0,5,2,2,5,5,2,8,2,3,5,4,8,2,0,4
%N A371936 Decimal expansion of Sum_{k>=0} (-1)^k / (2*(k+1)*(2*k+1)!).
%F A371936 Equals 1 - cos(1) = A371935/2 = 1 - A049470.
%F A371936 Equals 1/A206533. - _Hugo Pfoertner_, Apr 26 2024
%e A371936 0.459697694131860282599063392557023396267689579382077772...
%t A371936 s = N[Sum[(-1)^k/(2(k + 1) (2 k + 1)!), {k, 0, Infinity}], 120]
%t A371936 First[RealDigits[s]]
%o A371936 (PARI) 1 - cos(1) \\ _Stefano Spezia_, Apr 21 2025
%Y A371936 Cf. A049470, A206533, A371935.
%K A371936 nonn,cons
%O A371936 0,1
%A A371936 _Clark Kimberling_, Apr 24 2024