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A080642
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Cubefree taxicab numbers: the smallest cubefree number that is the sum of 2 cubes in n ways.
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3
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OFFSET
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1,1
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COMMENTS
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A necessary condition for the sum to be cubefree is that each pair of cubes be relatively prime.
If the sequence is infinite, then the Mordell-Weil rank of the elliptic curve of rational solutions to x^3 + y^3 = a(n) tends to infinity with n. In fact, the rank exceeds C*log(n) for some constant C>0 (see Silverman p. 339). - Jonathan Sondow, Oct 22 2013
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LINKS
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Table of n, a(n) for n=1..4.
J. H. Silverman, Taxicabs and Sums of Two Cubes, Amer. Math. Monthly, 100 (1993), 331-340.
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FORMULA
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a(n) >= A011541(n) for n > 0, with equality for n = 1, 2 (only?). - Jonathan Sondow, Oct 25 2013
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EXAMPLE
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2 = 1^3 + 1^3
1729 = 12^3 + 1^3 = 10^3 + 9^3
15170835645 = 2468^3 + 517^3 = 2456^3 + 709^3 = 2152^3 + 1733^3
1801049058342701083 = 1216500^3 + 92227^3 = 1216102^3 + 136635^3 = 1207602^3 + 341995^3 = 1165884^3 + 600259^3
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CROSSREFS
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Cf. A011541.
Sequence in context: A233132 A277389 A011541 * A108331 A263076 A162554
Adjacent sequences: A080639 A080640 A080641 * A080643 A080644 A080645
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KEYWORD
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hard,more,nonn
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AUTHOR
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Stuart Gascoigne (Stuart.G(AT)scoigne.com), Feb 28 2003
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STATUS
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approved
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