OFFSET
0,2
LINKS
T. D. Noe, Table of n, a(n) for n = 0..1000
FORMULA
a(n) = number of triples (i, j, k) with 1 <= i+j+k <= n and gcd(i, j, k) = 1.
Cumulative sums of A048240(k) for k>0.
EXAMPLE
a(2)=6: primary and secondary colors (Y^1, B^1, R^1, Y^1*B^1, Y^1*R^1, B^1*R^1).
MATHEMATICA
Accumulate[ Table[ Sum[ MoebiusMu[n/d]*(d + 1)*(d + 2)/2, {d, Divisors[n]}], {n, 0, 43}]] (* Jean-François Alcover, Jul 16 2012, after Vladeta Jovovic *)
CROSSREFS
KEYWORD
nonn,nice,easy
AUTHOR
EXTENSIONS
More terms from Robin Trew (trew(AT)hcs.harvard.edu).
STATUS
approved