 Wieferich sequence is a special type of Barker sequence.Every integer "k">1 has its own Wieferich sequence.To make a Wieferich sequence of an integer "k">1, start with a(1)="k", a("n") = the smallest prime "p" such that a("n"-1)"p"-1 = 1 (mod "p") but a("n"-1) ≠ 1 or -1 (mod "p").