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 A086465 #28 Feb 16 2025 08:32:50
%S A086465 3,7,2,1,6,3,5,7,6,3,8,5,6,0,1,6,1,5,5,5,5,7,7,3,2,9,3,1,8,0,2,4,2,1,
%T A086465 7,0,1,6,9,8,2,8,2,7,3,0,1,6,1,1,5,8,6,1,9,0,2,8,0,2,4,4,1,5,9,7,0,2,
%U A086465 4,4,8,6,1,8,4,4,5,2,7,8,4,5,4,4,5,9,6,1,0,5,8,7,8,8,8,7,9,8,2
%N A086465 Decimal expansion of (5 + 4*sqrt(5)*arcsch(2))/25.
%H A086465 D. H. Lehmer, <a href="http://www.jstor.org/stable/2322496">Interesting series involving the Central Binomial Coefficient</a>, Am. Math. Monthly 92, No. 7 (1985) 449-457.
%H A086465 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CentralBinomialCoefficient.html">Central Binomial Coefficient</a>.
%H A086465 Wikipedia, <a href="http://en.wikipedia.org/wiki/Inverse_hyperbolic_function#Series_expansions">Inverse hyperbolic function: Series expansions</a>.
%H A086465 <a href="/index/Tra#transcendental">Index entries for transcendental numbers</a>.
%F A086465 Equals Sum_{n>=1} (-1)^(n-1)/binomial(2*n,n).
%e A086465 0.37216357638560161555577...
%p A086465 2/625*(14*sqrt(5)*log((1+sqrt(5))/2)+5) ; # _R. J. Mathar_, Mar 04 2009
%t A086465 RealDigits[(5 + 4*Sqrt[5]*ArcSinh[1/2])/25, 10, 120][[1]] (* _Amiram Eldar_, May 25 2023 *)
%o A086465 (PARI) suminf(n=1, (-1)^(n-1)/binomial(2*n,n)) \\ _Michel Marcus_, Jul 31 2015
%o A086465 (PARI) asinh(.5)*sqrt(5)*.16+.2 \\ Use \p99 to get 99 digits. - _M. F. Hasler_, Jul 31 2015
%Y A086465 Cf. A086466, A086467, A086468.
%K A086465 nonn,cons
%O A086465 0,1
%A A086465 _Eric W. Weisstein_, Jul 21 2003
%E A086465 Corrected definition and digits by a factor of 25/24. - _R. J. Mathar_, Mar 04 2009