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 A240885 #21 Sep 02 2024 10:42:48
%S A240885 1,2,7,5,5,4,7,7,3,6,4,1,7,2,1,5,3,7,8,8,0,1,3,4,3,1,9,7,4,6,7,8,5,4,
%T A240885 7,9,0,7,3,0,7,8,1,4,3,7,4,9,4,7,2,6,1,4,3,9,4,4,8,7,3,2,6,4,6,3,1,6,
%U A240885 4,6,9,2,5,6,4,3,0,0,8,6,4,1,6,0,4,6,2,5,2,7,5,9,5,4,2,9,3,4,5,6
%N A240885 Decimal expansion of the unique positive solution of Integral_{0..x} exp(-t^2/2) dt = 1.
%H A240885 Steven Finch, <a href="https://web.archive.org/web/20150405060634/http://www.people.fas.harvard.edu/~sfinch/csolve/av.pdf">Pattern-Avoiding Permutations</a> [Internet archive]
%H A240885 Steven Finch, <a href="/A240885/a240885.pdf">Pattern-Avoiding Permutations</a> [Cached copy, with permission]
%F A240885 Solution to sqrt(Pi/2)*erf(x/sqrt(2)) = 1.
%e A240885 1.2755477364172...
%t A240885 RealDigits[Sqrt[2]*InverseErf[Sqrt[2/Pi]], 10, 100] // First
%o A240885 (PARI) a=sqrt(Pi/2); b=a-1; c=1/sqrt(2); solve(x=1,2, a*erfc(c*x)-b) \\ _Charles R Greathouse IV_, Sep 02 2024
%Y A240885 Cf. A052319, A071075, A111004, A200404, A263885.
%K A240885 nonn,cons
%O A240885 1,2
%A A240885 _Jean-François Alcover_, Apr 14 2014