Book excerpt: Papers on Smarandache function S(n), Erdos-Smarandache numbers, generalized intuitionistic fuzzy contra continuous functions and its applications, the asymptotic properties of triangular base sequence, linear operators preserving commuting pairs of matrices over semirings, two inequalities for the composition of arithmetic functions, compactness and proper maps in the category of generated spaces, and similar topics. Contributors: R. Ma, Y. Zhang, R. Dhavaseelan, M. Dragan, M. Bencze, Q. Yang, G. Mirhosseinkhani, C. Fu, S. S. Billing, B. Hazarika, and others.