Kotova, O. V. 2008. “Continuum Cardinality of the Set of Solutions of One Class of Equations That Contain the Function of Frequency of Ternary Digits of a Number”.
Ukrains’kyi Matematychnyi Zhurnal 60 (10): 1414–1421.
https://umj.imath.kiev.ua/index.php/umj/article/view/3255.