OFFSET
0,2
LINKS
T. D. Noe, Table of n, a(n) for n = 0..1000
FORMULA
EXAMPLE
a(2)=7: white, primary and secondary colors (null, 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}]] + 1 (* Jean-François Alcover, Oct 16 2013, after T. D. Noe *)
CROSSREFS
KEYWORD
nonn,easy,nice
AUTHOR
Jurjen N.E. Bos, N. J. A. Sloane, Robin Trew (trew(AT)hcs.harvard.edu)
STATUS
approved