Spyros S. Magliveras, Tran van Trung, Wandi Wei
Abstract
Let Σ = {0, 1} be the binary alphabet, and A = {0, 01, 11} be the set of three strings 0, 01, 11 over Σ. Let A* denote the Kleene closure of A, 0 the set of nonnegative integers, and + the set of positive integers. A sequence in A* is called a Jacobsthal binary sequence. Let J(n) denote the set of Jacobsthal binary sequences of length n. For k ∊ +, {s1, s2, . . . , sk} ⊂ 0, and n − 1 ≥ s1 > s2 > .. . > sk ≥ 0, let J1(n; s1, s2, . . . , sk) denote the subset J1(n; s1, s2, . . . , sk) = {an−1an−2 . . . a1a0 ∊ J(n) : asi = 1 (1 ≤ i ≤ k)}, of J(n), and let N1(n; s1, s2, . . . , sk) = |J1(n; s1, s2, . . . , sk)|. When k = 1, a formula for N1(n; s) has been derived recently. In this paper we consider the general case of N1(n; s1, s2, . . . , sk), and study some other special types of Jacobsthal binary sequences. Some identities involving these numbers are also given.