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 A260658 #51 Jul 19 2024 21:52:56
%S A260658 5,-7,23,-1,41,-25,59,-17,77,-43,95,-13,113,-61,131,-35,149,-79,167,
%T A260658 -11,185,-97,203,-53,221,-115,239,-31,257,-133,275,-71,293,-151,311,
%U A260658 -5,329,-169,347,-89,365,-187,383,-49,401,-205,419,-107,437,-223,455,-29,473
%N A260658 Numerators of a BBP-like formula for 4*Pi/sqrt(27).
%C A260658 4*Pi/sqrt(27) = Sum_{n >= 0} (-1/8)^n*(2/(3*n+1)+1/(3*n+2)).
%C A260658 The reduced Collatz function R applied to the numbers 6n+3: a(n) = R(6n+3), where R(k) = (3k+1)/2^r, with r as large as possible, yields an unsigned version of this sequence. - _Jonas Kaiser_, Jun 17 2024
%H A260658 Paolo Xausa, <a href="/A260658/b260658.txt">Table of n, a(n) for n = 0..1000</a>
%H A260658 David H. Bailey, <a href="https://www.davidhbailey.com/dhbpapers/bbp-formulas.pdf">A Compendium of BBP-Type Formulas for Mathematical Constants</a>.
%H A260658 David Brink, <a href="https://www.researchgate.net/publication/283579663_Nilakantha's_accelerated_series_for_pi">Nilakantha's accelerated series for pi</a>, Acta Arith. 171 (2015), 293-308.
%F A260658 a(n) = numerator((-1/8)^n*(2/(3*n+1)+1/(3*n+2))).
%t A260658 A260658[n_] := Numerator[(-1/8)^n*(2/(3*n + 1) + 1/(3*n + 2))];
%t A260658 Array[A260658, 100, 0] (* _Paolo Xausa_, Jun 19 2024 *)
%o A260658 (PARI) a(n) = numerator((-1/8)^n*(2/(3*n+1) + 1/(3*n+2))); \\ _Michel Marcus_, Nov 15 2015
%o A260658 (Magma) [Numerator((-1/8)^n*(2/(3*n+1)+1/(3*n+2))): n in [0..60]]; // _Vincenzo Librandi_, Nov 20 2015
%Y A260658 Cf. A073010, A260659 (denominators).
%K A260658 sign,frac
%O A260658 0,1
%A A260658 _David Brink_, Nov 13 2015
%E A260658 More terms from _Michel Marcus_, Nov 15 2015