%I A091648
%S A091648 8,8,1,3,7,3,5,8,7,0,1,9,5,4,3,0,2,5,2,3,2,6,0,9,3,2,4,9,7,9,7,9,2,3,0,
%T A091648 9,0,2,8,1,6,0,3,2,8,2,6,1,6,3,5,4,1,0,7,5,3,2,9,5,6,0,8,6,5,3,3,7,7,1,
%U A091648 8,4,2,2,2,0,2,6,0,8,7,8,3,3,7,0,6,8,9,1,9,1,0,2,5,6,0,4,2,8,5,6
%N A091648 Decimal expansion of ArcCosh[sqrt(2)], the inflection point of Sech[x].
%C A091648 Asymptotic growth constant in the exponent for the number of spanning 
               trees on the 2 X infinity strip on the square lattice. - R. J. Mathar 
               (mathar(AT)strw.leidenuniv.nl), May 14 2006
%C A091648 Equals sum_{n=1..infinity, n odd} binomial(2n,n)/(n*4^n) [D. H. Lehmer, 
               Am. Math. Monthly 92 (1985) 449] [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), 
               Mar 04 2009]
%H A091648 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               HyperbolicSecant.html">Hyperbolic Secant</a>
%H A091648 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               UniversalParabolicConstant.html">Universal Parabolic Constant</a>
%H A091648 R. Shrock and F. Y. Wu, <a href="http://dx.doi.org/10.1088/0305-4470/
               33/21/303">Spanning trees on graphs and lattices in d dimensions</
               a>, J Phys A: Math Gen 33 (2000) 3881-3902
%F A091648 ln(1 + sqrt(2)) - Jonathan Sondow (jsondow(AT)alumni.princeton.edu), 
               Mar 15 2005
%F A091648 (1/2)*ln(3+2*sqrt(2)) - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), 
               May 14 2006
%e A091648 0.88137358...
%Y A091648 Cf. A103710, A103711, A103712.
%Y A091648 Sequence in context: A056194 A110940 A141134 this_sequence A135707 A021923 
               A065465
%Y A091648 Adjacent sequences: A091645 A091646 A091647 this_sequence A091649 A091650 
               A091651
%K A091648 nonn,cons,easy
%O A091648 0,1
%A A091648 Eric Weisstein (eric(AT)weisstein.com), Jan 24, 2004