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 A254866 #31 Feb 16 2025 08:33:24
%S A254866 1,1,4,27,4096,759375,12230590464,140710042265625,
%T A254866 472769874482845188096,601016336033894136931640625,
%U A254866 697127546117424200558837760000000000,153133225508583375568553948649382367138671875,91653624689233987245068783089656480594395136000000000000
%N A254866 a(n) = (n!!)^n.
%H A254866 Eric Weisstein, <a href="https://mathworld.wolfram.com/DoubleFactorial.html">Double Factorial</a>, (MathWorld)
%F A254866 a(n) ~ Pi^(n/2) * n^(n*(n+1)/2) / exp(n^2/2 - 1/6) if n is even.
%F A254866 a(n) ~ 2^(n/2) * n^(n*(n+1)/2) / exp(n^2/2 - 1/6) if n is odd.
%t A254866 Table[(n!!)^n, {n, 0, 15}]
%Y A254866 Cf. A006882, A036740, A185141.
%Y A254866 Cf. A000165, A001147.
%K A254866 nonn,easy
%O A254866 0,3
%A A254866 _Vaclav Kotesovec_, Feb 19 2015