login
The OEIS is supported by
the many generous donors to the OEIS Foundation
.
Hints
(Greetings from
The On-Line Encyclopedia of Integer Sequences
!)
A213680
a(n) = 2*a(n-1)^2/3-3 with a(0)=6.
0
6, 21, 291, 56451, 2124476931, 3008934820234119171, 6035792501611554034238453484153151491, 24287194081673507672666338605180770497437885188248737771493963111463682051
(
list
;
graph
;
refs
;
listen
;
history
;
text
;
internal format
)
OFFSET
0,1
LINKS
Table of n, a(n) for n=0..7.
FORMULA
a(n) = 3*cosh(2^n*arccosh(2)).
a(n) = 3*
A002812
(n). [
Giovanni Resta
, Mar 04 2013]
EXAMPLE
a(1) = 2*a(0)^2/3-3 = 2*6^2/3-3 = 21,
a(2) = 2*a(1)^2/3-3 = 2*21^2/3-3 = 291,
a(3) = 2*a(2)^2/3-3 = 2*291^2/3-3 = 2*84681/3-3 = 56451.
Or, by the first formula:
a(3) = 3*cosh(2^3*arccosh(2)) = 56451,
a(4) = 3*cosh(2^4*arccosh(2)) = 2124476931.
PROG
(Sage)
var('x')
p=2*x^2/3-3
s=[6]
for i in [0..8]:
s=s+[p(s[i])]
show(s)
CROSSREFS
Cf.
A002812
.
Sequence in context:
A372137
A244299
A143049
*
A164643
A190275
A261844
Adjacent sequences:
A213677
A213678
A213679
*
A213681
A213682
A213683
KEYWORD
nonn
AUTHOR
Jose Eduardo Blazek
, Mar 04 2013
STATUS
approved
Lookup
|
Welcome
|
Wiki
|
Register
|
Music
|
Plot 2
|
Demos
|
Index
|
Browse
|
More
|
WebCam
Contribute new seq. or comment
|
Format
|
Style Sheet
|
Transforms
|
Superseeker
|
Recents
The OEIS Community
| Maintained by
The OEIS Foundation Inc.
License Agreements, Terms of Use, Privacy Policy.
.
Last modified July 30 15:11 EDT 2024. Contains 374761 sequences. (Running on oeis4.)