OFFSET
0,9
LINKS
Index entries for linear recurrences with constant coefficients, signature (0,1,1,2,-1,-2,-2,-1,2,1,1,0,-1).
FORMULA
a(n) = Sum_{k=1..floor(n/4)} Sum_{j=k..floor((n-k)/3)} Sum_{i=j..floor((n-j-k)/2)} [(j mod 2) = (i mod 2) = ((n-i-j-k) mod 2)], where [ ] is the (generalized) Iverson bracket.
G.f.: x^4/((x^2+x+1)*(x^2+1)^2*(x+1)^3*(x-1)^4). - Alois P. Heinz, Jan 19 2021
MATHEMATICA
Table[Sum[Sum[Sum[KroneckerDelta[Mod[i, 2], Mod[j, 2], Mod[n - i - j - k, 2]], {i, j, Floor[(n - j - k)/2]}], {j, k, Floor[(n - k)/3]}], {k, Floor[n/4]}], {n, 0, 80}]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wesley Ivan Hurt, Jan 19 2021
STATUS
approved