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Jul 7, 2013 at 18:27 history edited Alicia Garcia-Raboso CC BY-SA 3.0
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Nov 9, 2009 at 23:54 comment added Kevin Buzzard In fact the root we want is the one which is about -10^{87} and within 10^{-6} of an integer. The other roots are "random" complex numbers (not near integers, or even near the reals in general) of size about 10^5.
Nov 9, 2009 at 23:51 comment added Kevin Buzzard I tried this on a computer. The conclusion is that j(5*tau) is a root of an irreducible degree 6 polynomial with coefficient of the order of 10^{100}.
Nov 9, 2009 at 22:30 comment added David E Speyer I don't think $j(n \tau)$ should be an integer. I think that would indicate that the order $Z[n \tau]$ has trivial class group, and I'm pretty sure that's not true. But I'm rusty on how the elliptic curve/class field dictionary works for nonmaximal orders.
Nov 9, 2009 at 22:27 comment added Kevin Buzzard I think that the conclusion from this would in fact be that j(n.tau) satisfied a polynomial of low degree but with humungous coefficients. Computer calculation indicate that j(5.tau) is in fact not an integer for tau as above, although it is close to one.
Nov 9, 2009 at 22:08 history answered David Hansen CC BY-SA 2.5