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 A271880 #17 Feb 16 2025 08:33:33
%S A271880 1,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,
%T A271880 9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,7,8,3,3,7,
%U A271880 7,7,3,1,6,2,8,6,4,7,6,0,5,5,2,7,9,4,6,2,5,9,4,0,6,5,1,3,3,3,2,7,7,5,6,1,9
%N A271880 Decimal expansion of the probability that a random real number is evil.
%C A271880 A real number is said to be evil if the cumulative sum of its digits following the decimal point 'hits' the value 666. It is amazing how close this value is to 1/5 (the difference is in A271881).
%H A271880 Stanislav Sykora, <a href="/A271880/b271880.txt">Table of n, a(n) for n = 0..2000</a>
%H A271880 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/EvilNumber.html">Evil Number</a>.
%F A271880 Equals A100061(666)/A100062(666).
%e A271880 0.19999999999999999999999999999999999999999999999999999999999999978337...
%t A271880 RealDigits[SeriesCoefficient[(1 - x^9)/(x^10 - 10 x + 9), {x, 0, 665}], 10, 120][[1]] (* _Amiram Eldar_, May 24 2023 *)
%o A271880 (PARI) 0.0 + Vec(Ser((1-x^9)/(x^10-10*x+9),x,666))[666]
%Y A271880 Cf. A001019, A010734, A100061, A100062, A271881.
%K A271880 nonn,cons,base
%O A271880 0,2
%A A271880 _Stanislav Sykora_, Apr 16 2016