Csörgö, S., and W. B. Wu. “On Sums of Overlapping Products of Independent Bernoulli Random Variables”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 52, no. 9, Sept. 2000, pp. 1304-9, https://umj.imath.kiev.ua/index.php/umj/article/view/4537.