A028941 - OEIS

A028941

Denominator of X-coordinate of n*P where P is the generator [0,0] for rational points on curve y^2+y = x^3-x.

1, 1, 1, 1, 4, 1, 9, 25, 49, 16, 529, 841, 3481, 16641, 98596, 4225, 2337841, 13608721, 67387681, 264517696, 6941055969, 12925188721, 384768368209, 5677664356225, 61935294530404, 49020596163841, 16063784753682169

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OFFSET

1,5

COMMENTS

We can take P = P[1] = [x_1, y_1] = [0,0]. Then P[n] = P[1]+P[n-1] = [x_n, y_n] for n >= 2. Sequence gives denominators of the x_n. - N. J. A. Sloane, Jan 27 2022

Squares of terms in A006769 (or A006720).

REFERENCES

G. Everest, A. J. van der Poorten, I. Shparlinski and T. Ward, Recurrence Sequences: Examples and Applications, AMS Monographs, 2003

A. W. Knapp, Elliptic Curves, Princeton 1992, p. 77.

LINKS

Seiichi Manyama, Table of n, a(n) for n = 1..212

B. Mazur, Arithmetic on curves, Bull. Amer. Math. Soc. 14 (1986), 207-259; see p. 225.

FORMULA

This sequence satisfies the quadratic recurrence relation a(n)a(n-6)=-a(n-1)a(n-5)+2a(n-2)a(n-4)+2a(n-3)^2 which is a generalized Somos-6 relation. - Graham Everest (g.everest(AT)uea.ac.uk), Dec 16 2002

P=(0, 0), 2P=(1, 0), if kP=(a, b) then (k+1)P=(a'=(b^2-a^3)/a^2, b'=-1-b*a'/a).

PROG

(PARI) - see A028940.

CROSSREFS

Cf. A028940, A028942, A028943.

Sequence in context: A278350 A128626 A193963 * A364109 A348180 A176080

Adjacent sequences: A028938 A028939 A028940 * A028942 A028943 A028944

KEYWORD

nonn,frac

AUTHOR

N. J. A. Sloane

STATUS

approved