[seqfan] Re: How to generate A000047?
T. D. Noe
noe at sspectra.com
Mon Jan 19 19:34:46 CET 2009
>I have been trying to regenerate the sequence A000047 without any luck.
>
>
>
>http://www.research.att.com/~njas/sequences/A000047
>
>
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>I assume that the integers <= 2^n are one or greater, but n, x, and y are >=
>0.
>
>My biggest problem is determining if a given integer is of the form x^2 -
>2y^2.
I used Mathematica to solve the Pell equations x^2-2y^2=k and determined
that the number of k<=2^n begins
1,2,3,5,15,26,48
which agrees with the sequence. Not sure that this is the fastest method.
Tony
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