Periodic sequences
An infinite sequence {a_r ∶r≥1} of digits,which can be taken as 0 or 1, is periodic if, for some k ≥ 1, a_(r+k)= a_r for all r ≥ 1. The number k is called the period and any finite subsequence {a_(N+r) ∶1 ≤ r ≤k} is called a cycle. One might as well take N = 0 and focus on the first cycle a_1 ,a_2 ,…,a_k. The trivial sequence consisting entirely of 1s has period 1.