We show that for an elliptic divisibility sequence on a twist of the Fermat cubic, u 3 + v 3 = m, with m cube-free, all the terms beyond the first have a primitive divisor.
Statement of Main TheoremLet C denote a twist of the Fermat cubic,with m a non-zero rational number. If K denotes any field of characteristic zero, the set C(K) of projective K-rational points satisfying (1) forms an elliptic curve. With respect to the usual chord and tangent addition the set C(K) forms a group. The identity of the group is (−1, 1, 0) and the inverse of the point ( This paper is devoted to proving the following theorem.Theorem 1.2. Let C denote the elliptic curve in (1) with m ∈ Z assumed to be cube-free. Let W = (W n ) denote the sequence obtained as above from R ∈ C(Q), a non-torsion rational point. For all n > 1, the term W n has a primitive divisor.The sequence W = (W n ) is a divisibility sequence, which means that, for all m, n ∈ N,In line with recent developments [11, 12, 13, 14, 15, 16, 25, 26, 27] we define the sequence W = (W n ) to be an Elliptic Divisibility Sequence. Admittedly this stretches the definition originally used by Morgan Ward [29] but we believe it is a reasonable name for a divisibility sequence that arises from an elliptic curve.