|
|
A014980
|
|
a(n+1) = floor(a(n)/2) * ceiling(a(n)/2), a(0) = 5.
|
|
4
|
|
|
5, 6, 9, 20, 100, 2500, 1562500, 610351562500, 93132257461547851562500, 2168404344971008868014905601739883422851562500, 1175494350822287507968736537222245677818665556772087521508751706278417259454727172851562500
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,1
|
|
COMMENTS
|
A194079(n) gives number of digits of a(n).
|
|
LINKS
|
|
|
FORMULA
|
a(0) = 5; a(k+1) = floor(a(k)/2) * ceiling(a(k)/2).
|
|
EXAMPLE
|
6 = 2*3; 9 = 3*3; 20 = 4*5; ...
|
|
MATHEMATICA
|
NestList[Floor[#/2]Ceiling[#/2]&, 5, 10] (* Harvey P. Dale, Jul 10 2012 *)
|
|
PROG
|
(Haskell)
a014980 n = a014980_list !! n
a014980_list = iterate a002620 5
(Python)
from itertools import accumulate
def f(an, _): return (an//2)*((an+1)//2)
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,nice,easy
|
|
AUTHOR
|
Colin Sandon (sandon(AT)together.net)
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|