OFFSET
1,2
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..250
Eric Weisstein's World of Mathematics, Cubefree.
EXAMPLE
There are eleven cuboids with sides <= 4 having a cubefree volume: 1 X 1 X 1, 1 X 1 X 2, 1 X 1 X 3, 1 X 1 X 4, 1 X 2 X 2, 1 X 2 X 3, 1 X 3 X 3, 1 X 3 X 4, 2 X 2 X 3, 2 X 3 X 3 and 3 X 3 X 4 whereas 1 X 2 X 4, 1 X 4 X 4, 2 X 2 X 2, 2 X 2 X 4, 2 X 3 X 4, 2 X 4 X 4, 3 X 3 X 3 and 4 X 4 X 4 are not cubefree; therefore a(4)=11.
PROG
(Haskell)
a070073 n = length [() | x <- [1..n], y <- [1..x], z <- [1..y],
a212793 (x*y*z) == 1]
-- Reinhard Zumkeller, May 27 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Apr 21 2002
STATUS
approved