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%I #28 Nov 19 2016 14:43:47
%S 1,1,1,125,64,24389,2146689,274625,50202571769,4302115807744,
%T 1469451780501769,13528653463047586625,343216282443844010111,
%U 63061816101171948456692661,495133617181351428873673516736
%N a(n) = denominator of y-coordinate of (2n)*P where P is the generator for rational points on the curve y^2 + y = x^3 - x.
%H Seiichi Manyama, <a href="/A028939/b028939.txt">Table of n, a(n) for n = 1..86</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) = A028943(2n). - _Seiichi Manyama_, Nov 19 2016
%e 8P = (21/25, -69/125).
%Y Cf. A028936, A028937, A028938 (numerator), A028943.
%K nonn,frac
%O 1,4
%A _N. J. A. Sloane_
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