OFFSET
5,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 5..200
FORMULA
a(n) = 1/6 * [(x*y*z)^n] Product_{j>0} (1+x^j+y^j+z^j).
EXAMPLE
a(7) = 4: [7;6,1;5,2], [7;6,1;4,3], [7;5,2;4,3], [6,1;5,2;4,3].
MATHEMATICA
nmax = 30; p = 1; Do[p = Expand[p*(1 + x^j + y^j + z^j)]; p = Select[p, (Exponent[#, x] <= nmax) && (Exponent[#, y] <= nmax) && (Exponent[#, z] <= nmax) &], {j, 1, nmax}]; p = Select[p, Exponent[#, x] == Exponent[#, y] == Exponent[#, z] &]; Table[Coefficient[p, x^n*y^n*z^n]/6, {n, 5, nmax}] (* Vaclav Kotesovec, Apr 07 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, May 25 2015
STATUS
approved