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 A105532 #15 Feb 16 2025 08:32:57
%S A105532 1,9,7,3,9,5,5,5,9,8,4,9,8,8,0,7,5,8,3,7,0,0,4,9,7,6,5,1,9,4,7,9,0,2,
%T A105532 9,3,4,4,7,5,8,5,1,0,3,7,8,7,8,5,2,1,0,1,5,1,7,6,8,8,9,4,0,2,4,1,0,3,
%U A105532 3,9,6,9,9,7,8,2,4,3,7,8,5,7,3,2,6,9,7,8,2,8,0,3,7,2,8,8,0,4,4,1,1,2,6,2,8
%N A105532 Decimal expansion of arctan(1/5).
%H A105532 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Machin-LikeFormulas.html">Machin-Like Formulas</a>
%H A105532 <a href="/index/Tra#transcendental">Index entries for transcendental numbers</a>
%F A105532 4*arctan(1/5) - A105534 = Pi/4 (Machin's formula).
%F A105532 From _Amiram Eldar_, Aug 04 2020: (Start)
%F A105532 Equals Sum_{k>=0} (-1)^k/((2*k+1) * 5^(2*k+1)) = Sum_{k>=0} (-1)^k/A072172(k).
%F A105532 Equals Sum_{k>=1} arctan(1/(2*(k+2)^2)). (End)
%e A105532 0.197395559849880758370049765194790293447585103787852101517688940241033969...
%t A105532 RealDigits[ArcTan[1/5], 10, 100][[1]] (* _Amiram Eldar_, Aug 04 2020 *)
%o A105532 (PARI) atan(1/5) \\ _Michel Marcus_, Sep 24 2014
%Y A105532 Cf. A003881 (Pi/4), A072172, A105534 (arctan 1/239).
%K A105532 cons,nonn
%O A105532 0,2
%A A105532 Bryan Jacobs (bryanjj(AT)gmail.com), Apr 12 2005
%E A105532 Corrected position of decimal point in example. - _R. J. Mathar_, Feb 05 2009