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Sep 16, 2014 at 19:07 vote accept Will Jagy
Sep 16, 2014 at 19:07 history edited Will Jagy CC BY-SA 3.0
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Sep 16, 2014 at 3:43 history edited Will Jagy CC BY-SA 3.0
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Sep 16, 2014 at 3:18 history edited Venkataramana CC BY-SA 3.0
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Sep 16, 2014 at 3:07 history edited Will Jagy CC BY-SA 3.0
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Sep 16, 2014 at 2:48 comment added Will Jagy @FelipeVoloch, thanks. I will finish it with computer, I need to fiddle a bit for the prime $5$ because the 4th powers times coefficients get a bit too large for ordinary C++ integers. I see what you mean about your use of the word congruences, I think I noticed that in your comment at first, then i got distracted by David's answer.
Sep 16, 2014 at 2:45 comment added Felipe Voloch That's what I meant by congruences and it's not automatic. By pure thought, if the value of polynomial is divisible by a suitably high power of three, then the variables are divisible by three. To figure out what suitably high means, requires a calculation which I won't do.
Sep 16, 2014 at 2:39 comment added Will Jagy @FelipeVoloch, thanks. What about the first question, if the polynomial is divisble by $81,$ then all variables are divisible by $3?$ David suspects that is lots more work.
Sep 16, 2014 at 2:30 history edited Will Jagy CC BY-SA 3.0
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Sep 16, 2014 at 2:30 answer added David E Speyer timeline score: 12
Sep 16, 2014 at 2:30 comment added Felipe Voloch This is the norm of $a+b\sqrt{3}+c\sqrt{5}+d\sqrt{15}$ from the quartic field to the rationals, so it's a norm form. I don't think $1,\sqrt{3},\sqrt{5},\sqrt{15}$ form a basis of the ring of integers over the usual integers, so the congruences don't automatically follow from facts about norms, but it should not be hard to prove them that way. You can also use that to get information on numbers (integers?, rationals?) represented by it. I don't know how hard it would be to answer your last question.
Sep 16, 2014 at 2:07 history edited Will Jagy CC BY-SA 3.0
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Sep 16, 2014 at 1:58 history asked Will Jagy CC BY-SA 3.0