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 A193531 Number of integer solutions to the quartic elliptic curve y^2 = 5*x^4 - 4*n. 5
 2, 0, 0, 2, 0, 0, 0, 0, 0, 0, 6, 0, 0, 0, 0, 2, 0, 0, 2, 4, 0, 0, 0, 0, 2, 0, 0, 0, 4, 0, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 4, 0, 2, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The quintic x^5+n*x+m is reducible into cubic and quadratic factors if and only a(n) != 0. LINKS EXAMPLE We have following parametrization: (X^3 - d*X^2 + (d^2 - e)*X + (2*d*e - d^3))*(X^2 + d*X + e) =  -d^3*e + 2*d*e^2 + (-d^4 + 3*d^2*e - e^2)*X + X^5. Solving the equation (-d^4 + 3*d^2*e - e^2) = n for e we have e=(3*d^2 +/-sqrt(5*d^4 - 4*n))/2. So 5*d^4 - 4*n must be a perfect square (then y^2=5*x^4-4*n has at least one integer solution). PROG (MAGMA) [IntegralQuarticPoints([5, 0, 0, 0, -4*n]) : n in [1..55]]; CROSSREFS Cf. A193524, A193528. Sequence in context: A193033 A318253 A249772 * A093492 A139380 A128771 Adjacent sequences:  A193528 A193529 A193530 * A193532 A193533 A193534 KEYWORD nonn AUTHOR Artur Jasinski, Jul 29 2011 STATUS approved

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Last modified June 19 04:01 EDT 2021. Contains 345125 sequences. (Running on oeis4.)