EN
For any non-square 1 < D ≡ 0,1 (mod 4), Zagier defined $F_{k}(D;x) :=∑_{\substack{a,b,c ∈ ℤ, a <0\\ b^2-4ac=D}} max(0,(ax^2+bx+c)^{k-1})$. Here we use the theory of periods to give identities and congruences which relate various values of $F_k(D;x)$.