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 A091648 Decimal expansion of arccosh(sqrt(2)), the inflection point of sech(x). 18
 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, 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, 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 (list; constant; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS 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, May 14 2006 Arccosh(sqrt(2)) = (1/2)*log((sqrt(2)+1)/(sqrt(2)-1)) = log(tan(3*Pi/8)) = int(1/cos(x),x=0..Pi/4). Therefore, in Gerardus Mercator's (conformal) map this is the value of the ordinate y/R (R radius of the spherical earth) for latitude phi = 45 degrees north, or Pi/4. See, e.g., the Eli Maor reference, eqs. (5) and (6). This is the latitude of, e.g., the Mission Point Lighthouse, Michigan, U.S.A. - Wolfdieter Lang, Mar 05 2013 REFERENCES L. B. W. Jolley, Summation of Series, Dover (1961), Eq. (85) page 16-17. E. Maor, Trigonometric Delights, Princeton University Press, NJ, 1998, chapter 13, A Mapmaker's Paradise, pp. 163-180. LINKS Ivan Panchenko, Table of n, a(n) for n = 0..1000 D. H. Lehmer, Interesting Series Involving the Central Binomial Coefficient, Am. Math. Monthly 92 (1985) 449. R. Shrock and F. Y. Wu, Spanning trees on graphs and lattices in d dimensions, J Phys A: Math Gen 33 (2000) 3881-3902 Eric Weisstein's World of Mathematics, Hyperbolic Secant Eric Weisstein's World of Mathematics, Universal Parabolic Constant FORMULA Equals log(1 + sqrt(2)). - Jonathan Sondow, Mar 15 2005 Equals (1/2)*log(3+2*sqrt(2)). - R. J. Mathar, May 14 2006 Equals sum({n>=1, n odd} binomial(2*n,n)/(n*4^n) [see Lehmer link]. - R. J. Mathar, Mar 04 2009 Equals arcsinh(1), since arcsinh(x) = log(x+sqrt(x^2+1)). - Stanislav Sykora, Nov 01 2013 Equals asin(i)/i. - L. Edson Jeffery, Oct 19 2014 Equals (Pi/4) * 3F2(1/4, 1/2, 3/4; 1, 3/2; 1). - Jean-François Alcover, Apr 23 2015 EXAMPLE 0.8813735870195430252326093249797923090281603282616... MATHEMATICA RealDigits[Log[1 + Sqrt[2]], 10, 100][[1]] (* Alonso del Arte, Aug 11 2011 *) PROG (Maxima) fpprec : 100\$ ev(bfloat(log(1 + sqrt(2)))); /* Martin Ettl, Oct 17 2012 */ (PARI) asinh(1) \\ Michel Marcus, Oct 19 2014 CROSSREFS Cf. A103710, A103711, A103712, A181048. Sequence in context: A176155 A174127 A230153 * A135707 A021923 A296496 Adjacent sequences:  A091645 A091646 A091647 * A091649 A091650 A091651 KEYWORD nonn,cons,easy AUTHOR Eric W. Weisstein, Jan 24 2004 STATUS approved

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Last modified December 12 00:07 EST 2018. Contains 318052 sequences. (Running on oeis4.)