OFFSET
1,4
COMMENTS
Lim_{n -> infinity} a(n)/n = 6/Pi^2.
FORMULA
From Wesley Ivan Hurt, Jan 08 2022: (Start)
a(n) = Sum_{k=1..n-1} mu(2n-k)^2.
a(n) = Sum_{k=n+1..2n-1} mu(k)^2.
a(n) = Sum_{k=(n^2-n+2)/2..(n^2+n-2)/2} mu(A128076(k))^2. (End)
MATHEMATICA
Table[Count[Range[n+1, 2n-1], _?SquareFreeQ], {n, 80}] (* Harvey P. Dale, Mar 23 2019 *)
PROG
(PARI) for(n=1, 100, print1(sum(i=n+1, 2*n-1, issquarefree(i)), ", "))
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, May 02 2002
STATUS
approved