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 A257535 #15 May 24 2023 03:59:35
%S A257535 6,2,4,7,1,3,2,5,6,4,2,7,7,1,3,6,0,4,2,8,9,9,6,8,3,7,7,8,1,6,5,7,1,7,
%T A257535 8,4,2,8,6,2,4,6,7,4,4,9,4,9,4,4,1,1,2,0,0,1,6,0,1,7,5,2,2,5,8,7,2,2,
%U A257535 1,1,6,6,6,0,2,3,0,6,5,8,1,2,2,5,3,1,5,2,7,9,5,8,9,3,1,7,8,2,2,7,7,6,0,5,0
%N A257535 Decimal expansion of the imaginary part of -E_1(i), i being the imaginary unit.
%C A257535 E_1(z) = Integral_{t>=1}(exp(-t*z)/t) is the exponential integral.
%H A257535 Stanislav Sykora, <a href="/A257535/b257535.txt">Table of n, a(n) for n = 0..2000</a>
%H A257535 Wikipedia, <a href="http://en.wikipedia.org/wiki/Exponential_integral">Exponential integral</a>.
%F A257535 Equals imag(E_1(-i)).
%F A257535 Equals (Pi/2) - A099281.
%e A257535 0.6247132564277136042899683778165717842862467449494411200160175...
%t A257535 RealDigits[Pi/2 - SinIntegral[1], 10, 105][[1]] (* _Amiram Eldar_, May 24 2023 *)
%o A257535 (PARI) a = imag(-eint1(I))
%Y A257535 Cf. A099281, A099282, A099285.
%K A257535 nonn,cons
%O A257535 0,1
%A A257535 _Stanislav Sykora_, Apr 28 2015