[seqfan] How to generate A000047?

[Harry J. Smith]

I have been trying to regenerate the sequence A000047 without any luck.

 

http://www.research.att.com/~njas/sequences/A000047 

 

%I A000047 M0701 N0259

%S A000047
1,2,3,5,8,15,26,48,87,161,299,563,1066,2030,3885,7464,14384,27779,

%T A000047 53782,104359,202838,394860,769777,1502603,2936519,5744932

%N A000047 Number of integers <= 2^n of form x^2 - 2y^2.

%D A000047 D. Shanks and L. P. Schmid, Variations on a theorem of Landau.
Part I, 

               Math. Comp., 20 (1966), 551-569.

%H A000047 <a
href="http://www.research.att.com/~njas/sequences/Sindx_Qua.html#quadpop">

               Index entries for sequences related to populations of
quadratic forms</

               a>

%Y A000047 Sequence in context: A006982 A054539 A026702 this_sequence
A101172 A006544 

               A110536

%Y A000047 Adjacent sequences: A000044 A000045 A000046 this_sequence A000048
A000049 

               A000050

%K A000047 nonn

%O A000047 0,2

%A A000047 njas

 

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.

 

-Harry