OFFSET
1,1
COMMENTS
LINKS
Harry J. Smith, Table of n, a(n) for n = 1..1000
FORMULA
Sum_{n>=1} 1/a(n) = Pi^2/6 - 15/Pi^2. - Amiram Eldar, Jul 16 2020
PROG
(PARI) for(n=1, 55, if(issquarefree(n), n+1, print(n^2)))
(PARI) n=-1; for (m=1, 10^9, if (!issquarefree(m), write("b062320.txt", n++, " ", m^2); if (n==1000, break))) \\ Harry J. Smith, Aug 04 2009
(PARI) is(n)=issquare(n, &n) && !issquarefree(n) \\ Charles R Greathouse IV, Sep 18 2015
(Haskell)
a062320 = (^ 2) . a013929 -- Reinhard Zumkeller, Sep 03 2015
(Python)
from math import isqrt
from sympy import mobius
def A062320(n):
def f(x): return n+1+sum(mobius(k)*(x//k**2) for k in range(1, isqrt(x)+1))
def bisection(f, kmin=0, kmax=1):
while f(kmax) > kmax: kmax <<= 1
while kmax-kmin > 1:
kmid = kmax+kmin>>1
if f(kmid) <= kmid:
kmax = kmid
else:
kmin = kmid
return kmax
return bisection(f)**2 # Chai Wah Wu, Aug 31 2024
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jason Earls, Jul 05 2001
EXTENSIONS
More terms from Larry Reeves (larryr(AT)acm.org), Jul 11 2001
Offset corrected by Andrew Howroyd, Sep 18 2024
STATUS
approved