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 A295255 #9 Mar 27 2019 10:02:17
%S A295255 1,1,4,27,288,4145,75360,1655003,42628096,1260274689,42070233600,
%T A295255 1565308844539,64237925148672,2882670856605553,140430196702035968,
%U A295255 7380867094885024635,416320345406371921920,25084955259883686000257,1608058868442709001895936,109278344982307590211482971
%N A295255 Expansion of e.g.f. 2/(1 + sqrt(1 - 4*x*cos(x))).
%F A295255 E.g.f.: 1/(1 - x*cos(x)/(1 - x*cos(x)/(1 - x*cos(x)/(1 - x*cos(x)/(1 - ...))))), a continued fraction.
%F A295255 a(n) ~ sqrt(2 - 2*r*sqrt(16*r^2 - 1)) * n^(n-1) / (exp(n) * r^n), where r = A196605 = 0.2585985822541894903... is the root of the equation r*cos(r) = 1/4. - _Vaclav Kotesovec_, Nov 18 2017
%p A295255 a:=series(2/(1+sqrt(1-4*x*cos(x))),x=0,21): seq(n!*coeff(a,x,n),n=0..19); # _Paolo P. Lava_, Mar 27 2019
%t A295255 nmax = 19; CoefficientList[Series[2/(1 + Sqrt[1 - 4 x Cos[x]]), {x, 0, nmax}], x] Range[0, nmax]!
%t A295255 nmax = 19; CoefficientList[Series[1/(1 + ContinuedFractionK[-x Cos[x], 1, {k, 1, nmax}]), {x, 0, nmax}], x] Range[0, nmax]!
%Y A295255 Cf. A000108, A295237, A295254, A295256, A295257, A295258.
%K A295255 nonn
%O A295255 0,3
%A A295255 _Ilya Gutkovskiy_, Nov 18 2017