For any non-square 1 < D ≡ 0,1 (mod 4), Zagier defined . Here we use the theory of periods to give identities and congruences which relate various values of .
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-aa158-3-7, author = {Marie Jameson and Wissam Raji}, title = {Quadratic polynomials, period polynomials, and Hecke operators}, journal = {Acta Arithmetica}, volume = {161}, year = {2013}, pages = {287-297}, zbl = {1280.11027}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-aa158-3-7} }
Marie Jameson; Wissam Raji. Quadratic polynomials, period polynomials, and Hecke operators. Acta Arithmetica, Tome 161 (2013) pp. 287-297. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-aa158-3-7/