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a(n) = denominator of the X-coordinate of n*P where P is the generator [0,0] for rational points on the curve y^2 + y = x^3 + x^2.
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%I #18 Jul 08 2022 08:13:05

%S 1,1,1,1,4,9,1,49,121,400,361,7569,36481,38809,1036324,7187761,

%T 67092481,34117281,6607901521,68162766400,385083543601,9202249657441,

%U 209674135856641,4853089476046161,7099336433764,2600282294202480889,60193393235277536641,1371165544633857017809

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

%C 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.

%D D. Husemoller, Elliptic Curves, Springer, 1987, p. 28.

%D A. W. Knapp, Elliptic Curves, Princeton, 1992, p. 64.

%o (PARI) See A350622.

%Y Cf. A028940-A028943, A350622-A350625.

%K nonn,frac

%O 1,5

%A _N. J. A. Sloane_, Jan 27 2022