%I A000831
%S A000831 1,2,4,16,80,512,3904,34816,354560,4063232,51733504,724566016,
%T A000831 11070525440,183240753152,3266330312704,62382319599616,
%U A000831 1270842139934720,27507470234550272,630424777638805504
%N A000831 Expansion of (1+tan x)/(1-tan x).
%D A000831 D. Dumont, Further triangles of Seidel-Arnold type and continued fractions 
               related to Euler and Springer numbers, Adv. Appl. Math., 16 (1995), 
               275-296.
%H A000831 R. J. Mathar, <a href="b000831.txt">Table of n, a(n) for n = 0..83</a>
%F A000831 E.g.f.: tan(x+Pi/4).
%e A000831 (1+tan x)/(1-tan x)=1+2x/1!+4x^2/2!+16x^3/3!+80x^4/4!+512x^5/5!+...
%p A000831 A000831 := (1+tan(x))/(1-tan(x)) : for n from 0 to 200 do printf("%d 
               %d ",n,n!*coeftayl(A000831,x=0,n)) ; end: - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), 
               Nov 19 2006
%o A000831 (PARI) a(n)=if(n<1,!n,n!*polcoeff(1+2/(1/tan(x+x*O(x^n))-1),n))
%Y A000831 Bisections: A002436 and A012393.
%Y A000831 Cf. A155100.
%Y A000831 Sequence in context: A027436 A025225 A115125 this_sequence A000090 A013115 
               A007171
%Y A000831 Adjacent sequences: A000828 A000829 A000830 this_sequence A000832 A000833 
               A000834
%K A000831 nonn
%O A000831 0,2
%A A000831 N. J. A. Sloane (njas(AT)research.att.com).