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 A021243 #29 Jul 28 2025 16:56:05 %S A021243 0,0,4,1,8,4,1,0,0,4,1,8,4,1,0,0,4,1,8,4,1,0,0,4,1,8,4,1,0,0,4,1,8,4, %T A021243 1,0,0,4,1,8,4,1,0,0,4,1,8,4,1,0,0,4,1,8,4,1,0,0,4,1,8,4,1,0,0,4,1,8, %U A021243 4,1,0,0,4,1,8,4,1,0,0,4,1,8,4,1,0,0,4,1,8,4,1,0,0,4,1,8,4,1,0 %N A021243 Decimal expansion of 1/239. %H A021243 Joerg Arndt, <a href="http://jjj.de/arctan/arctanpage.html">Arctan relations for Pi</a> %H A021243 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Machin-LikeFormulas.html">Machin-Like Formulas</a> %H A021243 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,0,0,1). %F A021243 From _Jean-François Alcover_, Sep 14 2015: (Start) %F A021243 Pi = 16 arctan(1/5) - 4 arctan(1/239) [Machin's formula], %F A021243 arctan(1/239) = arctan(1/70) - arctan(1/99) = arctan(1/408) + arctan(1/577), %F A021243 1/239 = 4649 / 1111111. (End) %t A021243 First[RealDigits[1/239, 10, 100, -1]] (* _Paolo Xausa_, Jul 28 2025 *) %K A021243 nonn,cons,easy %O A021243 0,3 %A A021243 _N. J. A. Sloane_