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 A306858 #48 Nov 12 2021 12:21:11
%S A306858 7,2,4,7,7,8,4,5,9,0,0,7,0,7,6,3,3,1,8,1,8,2,2,7,9,6,7,6,0,6,2,1,6,1,
%T A306858 6,6,3,1,2,1,3,2,9,3,0,6,2,3,8,1,7,4,4,9,0,7,2,8,8,8,3,3,6,6,1,9,7,6,
%U A306858 9,5,8,9,6,0,9,8,6,0,7,9,9,7,6,1,8,0,0,7,1,2,6,5,0,2,0,3,6,0,1,4,4,5,8,3,3,1,8,9,7,1
%N A306858 Decimal expansion of 1 - 1/(1*3) + 1/(1*3*5) - 1/(1*3*5*7) + ...
%F A306858 Equals sqrt(Pi/(2*exp(1)))*erfi(1/sqrt(2)), where erfi is the imaginary error function.
%F A306858 Equals (1/sqrt(e)) * Sum_{k>=0} 1/(2^k * k! * (2*k+1)) = 1/(sqrt(e)) * Sum_{k>=0} 1/A014481(k). - _Amiram Eldar_, Nov 12 2021
%F A306858 Equals 1/(1+A113014). - _Jon Maiga_, Nov 12 2021
%e A306858 0.7247784590070763318182279676062161663121329...
%t A306858 RealDigits[Sqrt[Pi/(2 Exp[1])] Erfi[1/Sqrt[2]], 10, 110] [[1]]
%t A306858 RealDigits[Sqrt[2] DawsonF[1/Sqrt[2]], 10, 110] [[1]]
%Y A306858 Cf. A001147, A014481, A060196, A068996, A092605, A113014.
%K A306858 nonn,cons
%O A306858 0,1
%A A306858 _Ilya Gutkovskiy_, Jun 24 2019