login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A185190 E.g.f. satisfies: A(x) = x + arcsinh(A(x))^2. 1
1, 2, 12, 112, 1440, 23648, 473088, 11164032, 303624960, 9351301632, 321717276672, 12228424826880, 508916576243712, 23016333612318720, 1124014843389984768, 58949533609403842560, 3304473379374295744512, 197167421810210663301120, 12476358616574849161101312 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Radius of convergence of the e.g.f. A(x) is r = 0.2767308231516982...,

where r and A(r) satisfy: r = A(r) - (1 + A(r)^2)/4 and

A(r) = sinh( sqrt(1 + A(r)^2)/2 ), so that A(r) = 0.6241087588791013...

LINKS

Table of n, a(n) for n=1..19.

FORMULA

E.g.f. satisfies:

(1) A(x) = Series_Reversion( x - arcsinh(x)^2 ).

(2) A(x) = x + Sum_{n>=1} d^(n-1)/dx^(n-1) arcsinh(x)^(2*n) / n!.

(3) A(x) = x*exp( Sum_{n>=1} d^(n-1)/dx^(n-1) (arcsinh(x)^(2*n)/x) / n! ).

(4) A'(x) = sqrt(1+A(x)^2) / (sqrt(1+A(x)^2) - 2*arcsinh(A(x))).

a(n) ~ n^(n-1) * sqrt((1+s^2)/(2-s)) / (exp(n) * ((4*s-1-s^2)/4)^(n-1/2)), where s = 0.62410875887910134116443... is the root of the equation 2*log(s+sqrt(1+s^2)) = sqrt(1+s^2). - Vaclav Kotesovec, Jan 11 2014

EXAMPLE

E.g.f.: A(x) = x + 2*x^2/2! + 12*x^3/3! + 112*x^4/4! + 1440*x^5/5! + ...

Related expansions:

arcsinh(A(x)) = x + 2*x^2/2! + 11*x^3/3! + 100*x^4/4! + 1269*x^5/5! + ...

arcsinh(A(x))^2 = 2*x^2/2! + 12*x^3/3! + 112*x^4/4! + 1440*x^5/5! + ...

Series expressions:

A(x) = x + arcsinh(x)^2 + d/dx arcsinh(x)^4/2! + d^2/dx^2 arcsinh(x)^6/3! + d^3/dx^3 arcsinh(x)^8/4! + ...

log(A(x)/x) = arcsinh(x)^2/x + d/dx (arcsinh(x)^4/x)/2! + d^2/dx^2 (arcsinh(x)^6/x)/3! + d^3/dx^3 (arcsinh(x)^8/x)/4! + ...

MATHEMATICA

Rest[CoefficientList[InverseSeries[Series[x - ArcSinh[x]^2, {x, 0, 20}], x], x] * Range[0, 20]!] (* Vaclav Kotesovec, Jan 11 2014 *)

PROG

(PARI) {a(n)=local(A=x+O(x^n)); for(i=0, n, A=x + asinh(A)^2); n!*polcoeff(A, n)}

(PARI) {a(n)=n!*polcoeff(serreverse(x-asinh(x+x*O(x^n))^2), n)}

for(n=1, 26, print1(a(n), ", "))

(PARI) {Dx(n, F)=local(D=F); for(i=1, n, D=deriv(D)); D}

{a(n)=local(A=x); A=x+sum(m=1, n, Dx(m-1, asinh(x+x*O(x^n))^(2*m)/m!)); n!*polcoeff(A, n)}

(PARI) {Dx(n, F)=local(D=F); for(i=1, n, D=deriv(D)); D}

{a(n)=local(A=x+x^2+x*O(x^n)); A=x*exp(sum(m=1, n, Dx(m-1, asinh(x+x*O(x^n))^(2*m)/x/m!)+x*O(x^n))); n!*polcoeff(A, n)}

CROSSREFS

Cf. A143136, A205886, A214431.

Sequence in context: A124213 A143134 A214225 * A227460 A316651 A330654

Adjacent sequences:  A185187 A185188 A185189 * A185191 A185192 A185193

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Feb 05 2012

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 29 02:19 EDT 2020. Contains 333104 sequences. (Running on oeis4.)