OFFSET
1,2
LINKS
Eric M. Schmidt, Table of n, a(n) for n = 1..1000
J. E. Nymann and W. J. Leahey, On the probability that an integer chosen according to the binomial distribution be k-free, Rocky Mountain Journal of Mathematics 7 (1977), no. 4, 769-774.
FORMULA
a(n) ~ 2^n/zeta(2). [Take p = 1/2 in Nymann and Leahey.]
PROG
(Sage) def A235268(n) : return sum(binomial(n, k) for k in range(1, n+1) if is_squarefree(k))
(PARI) a(n) = sum(k=1, n, if (issquarefree(k), binomial(n, k), 0)); \\ Michel Marcus, Jul 16 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Eric M. Schmidt, Jul 15 2014
STATUS
approved