login
Cubes which are not the sum of three squares.
4

%I #10 Dec 26 2017 03:22:51

%S 343,3375,12167,21952,29791,59319,103823,166375,216000,250047,357911,

%T 493039,658503,778688,857375,1092727,1367631,1404928,1685159,1906624,

%U 2048383,2460375,2924207,3442951,3796416,4019679,4657463,5359375

%N Cubes which are not the sum of three squares.

%C This sequence was inspired by e-mail from Ray Chandler, Nov 07 2007

%H Robert Israel, <a href="/A134738/b134738.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A004215(n)^3. [From _Ray Chandler_, Jan 29 2009]

%p N:= 10^10: # to get all terms <= N

%p sort([seq(seq(4^(3*i) * (8*j + 7)^3, j = 0 .. floor((N^(1/3)/4^i - 7)/8)), i = 0 .. floor(log[4](N^(1/3))))]); # _Robert Israel_, Dec 26 2017

%t b = Table[x^3, {x, 1, 300}]; a = {}; Do[Do[Do[AppendTo[a, (x^2 + y^2 + z^2)^3], {x, 0, 30}], {y, 0, 30}], {z, 0, 30}]; Union[a]; Complement[b, a] (*Artur Jasinski*)

%t Select[Range[200]^3,SquaresR[3,#]==0&] (* _Harvey P. Dale_, Feb 03 2015 *)

%Y Cf. A004215, A134739.

%K nonn

%O 1,1

%A _Artur Jasinski_, Nov 07 2007

%E Extended by _Ray Chandler_, Jan 29 2009