OFFSET
1,3
COMMENTS
If two parallel faces of the inscribed cube are parallel XOY-plane and other two pairs are parallel planes x=y and x=-y respectively we'll have another sequence.
EXAMPLE
For n=3 we have 8 points between the defined cube and its inscribed sphere:
(-2,-2,-2)
(-2,-2, 2)
(-2, 2,-2)
(-2, 2, 2)
( 2,-2,-2)
( 2,-2, 2)
( 2, 2,-2)
( 2, 2, 2)
PROG
(Python)
for n in range (1, 42):
count=0
n2 = n*n
for x in range(-n+1, n):
for y in range(-n+1, n):
for z in range(-n+1, n):
if x*x+y*y+z*z > n2:
count += 1
print(count)
(PARI) a(n) = sum(x=-n+1, n-1, sum(y=-n+1, n-1, sum(z=-n+1, n-1, x*x+y*y+z*z>n^2))); \\ Michel Marcus, Jun 23 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Kirill Ustyantsev, Apr 29 2018
STATUS
approved