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

 

Logo

Annual appeal: Please make a donation to keep the OEIS running! Over 6000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A160143 A "look-alike" of the coefficients of the series for x/cos(x). 2
1, 3, 25, 427, 12465, 555731, 35135945, 2990414715, 329655706465, 45692713833379, 1111113564712575, 1595024111042171723, 387863354088927172625, 110350957750914345093747 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

The first difference with sequence A009843 (expansion of x/cos(x)) occurs at a(10). An explanation can be found in the "look-alike" of the numerators of (2*n+1)/(4^(2*n+1)-2^(2*n+1)) with the odd numbers 2n+1 (cf. A160144).

A156769 describes a similar "look-alike" with A036279 (expansion of tan(x)).

LINKS

Table of n, a(n) for n=0..13.

MAPLE

a := n -> (-1)^iquo(n, 2)*euler(n)*(n+1)/(4^(n+1)-2^(n+1));

seq(numer(a(2*n)), n=0..13);

CROSSREFS

Cf. A009843, A160144, A160145, A036279, A156769.

Sequence in context: A143925 A245309 A074708 * A009843 A182962 A223076

Adjacent sequences:  A160140 A160141 A160142 * A160144 A160145 A160146

KEYWORD

frac,nonn

AUTHOR

Peter Luschny, May 03 2009

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 November 19 10:44 EST 2017. Contains 294936 sequences.