%I #21 Nov 20 2016 06:48:40
%S 0,-1,1,-5,-20,116,-3741,8385,-239785,-59997896,1849037896,
%T -270896443865,-16683000076735,2786836257692691,-3148929681285740316,
%U 342115756927607927420,-280251129922563291422645,-804287518035141565236193151
%N Numerator of x-coordinate of (2n+1)*P where P is the generator for rational points on the curve y^2 + y = x^3 - x.
%H Seiichi Manyama, <a href="/A028944/b028944.txt">Table of n, a(n) for n = 0..105</a>
%H B. Mazur, <a href="https://doi.org/10.1090/S0273-0979-1986-15430-3">Arithmetic on curves</a>, Bull. Amer. Math. Soc. 14 (1986), 207-259; see p. 225.
%F 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).
%F a(n) = A028940(2n+1). - _Seiichi Manyama_, Nov 20 2016
%e 7P = (-5/9, 8/27).
%Y Cf. A028940, A028945.
%K sign,frac
%O 0,4
%A _N. J. A. Sloane_