VarbanetsP. D., and DadayanZ. Y. “On the Average Value of a Generalized Pillai Function over $\mathbb{Z} [i]$ in the Arithmetic Progression”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 65, no. 6, June 2013, pp. 755–764, https://umj.imath.kiev.ua/index.php/umj/article/view/2460.