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 A246457 Given m the n-th cubefree number, A004709(n); a(n) is the class number of field Q(m^(1/3)). 0
 1, 1, 1, 1, 1, 3, 1, 1, 2, 1, 3, 3, 2, 1, 1, 3, 3, 3, 3, 1, 1, 3, 3, 1, 3, 3, 1, 3, 3, 1, 3, 3, 6, 1, 3, 12, 1, 1, 1, 2, 3, 1, 3, 3, 1, 1, 6, 6, 1, 3, 6, 3, 6, 18, 6, 6, 3, 1, 9, 1, 3, 3 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,6 COMMENTS The smallest m for which Q(m^(1/3)) not a unique factorization domain is m = 6, for which the corresponding field has class number 3. The table in Alaca & Williams includes 63 but excludes 18 and other cubefree but not squarefree numbers. It is clear that cubefree perfect squares are omitted from their table because on p. 328 they assert that Q((k^2)^(1/3)) = Q(k^(1/3)). REFERENCES Şaban Alaca & Kenneth S. Williams, Introductory Algebraic Number Theory. Cambridge: Cambridge University Press (2004): 325-329, Examples 12.6.8 & 12.6.9, Table 9. LINKS Lawrence C. Washington, Class Numbers of the Simplest Cubic Fields, Mathematics of Computation, Vol. 48, No. 177 (January 1987): 371 - 384. EXAMPLE a(8) = 1 because the eighth cubefree number is 9 and Q(9^(1/3)) has class number 1. a(9) = 2 because the ninth cubefree number is 10 and Q(10^(1/3)) has class number 2. CROSSREFS Cf. A004709, A005472, A242867. Sequence in context: A080847 A270572 A095276 * A089338 A153066 A126209 Adjacent sequences:  A246454 A246455 A246456 * A246458 A246459 A246460 KEYWORD nonn,more AUTHOR Alonso del Arte, Aug 26 2014 STATUS approved

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Last modified January 18 11:33 EST 2019. Contains 319271 sequences. (Running on oeis4.)