login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A008775 Expansion of 2(1 + cos x cosh x )^-1. 1
1, 2, 272, 261392, 923578112, 8687146706432, 179207715900772352, 7123449535546491471872, 497301503279765920504020992, 56869795869126246818618490355712, 10089974849557868979545831504092332032, 2659150134955694814127423122143061660925952 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

REFERENCES

Goulden and Jackson, Combin. Enum., Wiley, 1983 p. 287.

LINKS

Table of n, a(n) for n=0..11.

FORMULA

a(n) ~ 8 * (4*n)! / ((cosh(r)*sin(r) - cos(r)*sinh(r)) * r^(4*n+1)), where r = 1.875104068711961166445308241... is the root of the equation cosh(r)*cos(r) = -1. - Vaclav Kotesovec, Sep 15 2014

MATHEMATICA

Table[(CoefficientList[Series[2/(1 + Cos[x]*Cosh[x]), {x, 0, 60}], x] * Range[0, 60]! )[[n]], {n, 1, 61, 4}] (* Vaclav Kotesovec, Sep 15 2014 *)

CROSSREFS

Cf. A101921.

Sequence in context: A007512 A048534 A135696 * A237993 A174710 A200168

Adjacent sequences:  A008772 A008773 A008774 * A008776 A008777 A008778

KEYWORD

nonn

AUTHOR

N. J. A. Sloane.

EXTENSIONS

More terms from Vaclav Kotesovec, Sep 15 2014

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified February 20 22:25 EST 2018. Contains 299387 sequences. (Running on oeis4.)