A202537 - OEIS

A202537

Decimal expansion of x satisfying e^x-e^(-2x)=1.

3, 8, 2, 2, 4, 5, 0, 8, 5, 8, 4, 0, 0, 3, 5, 6, 4, 1, 3, 2, 9, 3, 5, 8, 4, 9, 9, 1, 8, 4, 8, 5, 7, 3, 9, 3, 7, 5, 9, 4, 1, 6, 4, 2, 2, 4, 2, 0, 1, 9, 5, 4, 3, 0, 0, 2, 9, 2, 8, 3, 9, 3, 8, 3, 6, 1, 6, 5, 4, 8, 9, 0, 5, 5, 0, 5, 8, 3, 1, 8, 2, 0, 1, 7, 0, 1, 3, 5, 0, 8, 5, 1, 5, 9, 0, 0, 9, 1, 2

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OFFSET

0,1

COMMENTS

If u>0 and v>0, there is a unique number x satisfying e^(ux)-e^(-vx)=1. Guide to related sequences, with graphs included in Mathematica programs:

u.... v.... x

1.... 1.... A002390

1.... 2.... A202537

1.... 3.... A202538

2.... 1.... A202539

3.... 1.... A202540

2.... 2.... A202541

3.... 3.... A202542

1/2..1/2... A202543

Suppose that f(x,u,v) is a function of three real variables and that g(u,v) is a function defined implicitly by f(g(u,v),u,v)=0. We call the graph of z=g(u,v) an implicit surface of f. For an example related to A202537, take f(x,u,v)=e^(ux)-e^(-vx)-1 and g(u,v) = a nonzero solution x of f(x,u,v)=0. If there is more than one nonzero solution, care must be taken to ensure that the resulting function g(u,v) is single-valued and continuous. A portion of an implicit surface is plotted by Program 2 in the Mathematica section.

LINKS

Table of n, a(n) for n=0..98.

EXAMPLE

x=0.382245085840035641329358499184857393759416422...

MATHEMATICA

(* Program 1: A202537 *)

u = 1; v = 2;

f[x_] := E^(u*x) - E^(-v*x); g[x_] := 1

Plot[{f[x], g[x]}, {x, -2, 2}, {AxesOrigin -> {0, 0}}]

r = x /. FindRoot[f[x] == g[x], {x, .3, .4}, WorkingPrecision -> 110]

RealDigits[r] (* A202537 *)

(* Program 2: implicit surface for e^(ux)-e(-vx)=1 *)