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 A167199 #20 Aug 24 2025 03:45:14
%S A167199 1,-2,7,-36,246,-2100,21510,-257040,3510360,-53933040,920694600,
%T A167199 -17288964000,354169292400,-7859862410400,187846741882800,
%U A167199 -4810116703392000,131382125482608000,-3812816394747360000,117159925012065936000,-3800085546956707008000,129743036125975752480000
%N A167199 First column of A167196.
%C A167199 Limiting ratio 2+n*a(n-1)/a(n) converges to A002193.
%F A167199 Conjecture: E.g.f.: 2/(2+4*x+x^2) = G(0)/(1+x) where G(k) = 1 - x/((1+x) - x*(1+x)/(x - (1+x)*2/G(k+1) )); (recursively defined continued fraction). - _Sergei N. Gladkovskii_, Dec 28 2012.
%F A167199 a(n) ~ n! * (-1)^n * (1+sqrt(2))/2 * (1+1/sqrt(2))^n. - _Vaclav Kotesovec_, Oct 08 2013
%F A167199 a(n) = ((sqrt(2) + 1)^(n+1) - (sqrt(2) - 1)^(n+1)) * n! * (-1)^n / 2^(n/2 + 1). - _Enrique Navarrete_, Aug 19 2025
%t A167199 CoefficientList[Series[2/(2+4*x+x^2), {x, 0, 20}], x]* Range[0, 20]! (* _Vaclav Kotesovec_, Oct 08 2013 *)
%Y A167199 Cf. A167196, A002193.
%K A167199 sign,changed
%O A167199 0,2
%A A167199 _Mats Granvik_, Oct 30 2009
%E A167199 More terms from _Amiram Eldar_, May 05 2024