|
|
A129843
|
|
a(n) = number of positive integers that are <= n and are coprime to n!! (n!! = A006882(n)).
|
|
1
|
|
|
1, 1, 2, 2, 3, 2, 3, 3, 4, 2, 4, 3, 4, 3, 4, 3, 5, 4, 5, 5, 5, 4, 5, 5, 5, 4, 5, 4, 5, 5, 5, 6, 6, 5, 6, 5, 6, 5, 6, 5, 6, 6, 6, 7, 6, 6, 6, 7, 6, 7, 6, 7, 6, 8, 6, 8, 6, 7, 6, 8, 6, 8, 6, 8, 7, 8, 7, 9, 7, 9, 7, 10, 7, 10, 7, 10, 7, 10, 7, 11
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,3
|
|
LINKS
|
|
|
FORMULA
|
If n > 2 is even, a(n) = 1 + A056171(n). (End)
|
|
MAPLE
|
f:= proc(n) local t;
if n::odd then ilog2(n)+1
else 1+numtheory:-pi(n) - numtheory:-pi(n/2)
fi
end proc:
f(2):= 1:
|
|
MATHEMATICA
|
a[n_]:=Module[{}, co=0; For[i=1, i<n+1, i++, If[GCD[n!!, i]==1, co++ ]]; co]; Table[a[n], {n, 1, 80}] (* Stefan Steinerberger, Jun 05 2007 *)
Table[Total[Boole[CoprimeQ[n!!, Range[n]]]], {n, 80}] (* Harvey P. Dale, Dec 12 2022 *)
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|