Rational torsion in the family x times x plus one times x plus m squared

ID: rational-torsion-in-the-family-x-times-x-plus-one-times-x-plus-m-squared

For integral , suppose has good reduction at five or seven. At five, ; at seven, or . Each resulting reduced elliptic curve has eight points. These restrictions follow from and : if an odd prime divides , the j-invariant of an elliptic curve has negative valuation. The torsion-freeness of the formal group over Qp for odd p bounds the whole rational torsion by eight. The point doubles to , and is an independent 2-torsion point. These generate the stated group of order eight.

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