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 A348131 #27 Mar 31 2022 12:46:25
%S A348131 1,4,7,272,211,51012,14197,18640960,1690981,11225320100,313968931,
%T A348131 10079828372880,83828316391,12627774819845668,30436810578889,
%U A348131 21046391759976988928,14425381885981321,45032132922921758270916,8649148282327007911,120314227994702795221920400
%N A348131 a(n) is the numerator of the relativistic sum of n velocities of 1/n, in units where the speed of light is 1.
%H A348131 Amiram Eldar, <a href="/A348131/b348131.txt">Table of n, a(n) for n = 1..387</a>
%H A348131 Wikipedia, <a href="https://en.wikipedia.org/wiki/Velocity-addition_formula">Velocity-addition formula</a>.
%F A348131 a(n)/A348132(n) = tanh(n * arctanh(1/n)).
%F A348131 Lim_{n->oo} a(n)/A348132(n) = tanh(1) (A073744).
%F A348131 a(2n-1) = n^(2n-1) - (n-1)^(2n-1) and a(2n) = ((2n+1)^(2n) - (2n-1)^(2n)) / 2. - _Thomas Ordowski_, Feb 12 2022
%e A348131 The fractions begins with 1, 4/5, 7/9, 272/353, 211/275, 51012/66637, 14197/18571, 18640960/24405761, 1690981/2215269, 11225320100/14712104501, ...
%e A348131 For n = 2, the sum of two velocities of 1/2 is (1/2 + 1/2)/(1 + (1/2)*(1/2)) = 4/5, thus a(2) = 4.
%t A348131 f[n_] := Module[{s = 1/n}, Do[s = (s + 1/n)/(1 + s/n), {k, 1, n - 1}]; s]; Numerator @ Array[f, 20]
%Y A348131 Cf. A073744, A348051, A348052, A348132 (denominators).
%K A348131 nonn,frac
%O A348131 1,2
%A A348131 _Amiram Eldar_, Oct 01 2021