Elements of the theory of numbers. From Euclid to Lucas : elementary theorems revisited -- Solutions of congruences, primitive roots -- The Chinese remainder theorem -- Mobius inversion -- Quadratic residues (mod r) (r > 1) -- Decomposition of a number as a sum of two or four squares -- Dirichlet algebra of arithmetical functions -- Modular arithmetical functions -- A generalization of ramanujan sums -- Ramanujan expansions of multiplicative arithmetic functions -- Selected topics in algebra. On the uniqueness of a group of order r (r > 1) -- Quadratic reciprocity in a finite group -- Commutative rings with unity -- Noetherian and Artinian rings -- Glimpses of the theory of algebraic numbers. Dedekind domains -- Algebraic number fields -- Vaidyanathaswamy's class-division of integers modulo r -- Burnside's lemma and a few of its applications -- On cyclic codes of length n over Fq -- An analogue of the Goldbach problem.