|
|
A274274
|
|
Number of ordered ways to write n as x^3 + y^2 + z^2, where x,y,z are nonnegative integers with y <= z.
|
|
7
|
|
|
1, 2, 2, 1, 1, 2, 1, 0, 2, 3, 3, 1, 1, 2, 1, 0, 2, 3, 3, 1, 1, 2, 0, 0, 1, 3, 4, 2, 2, 2, 1, 1, 2, 3, 2, 2, 2, 4, 1, 0, 3, 2, 2, 1, 2, 3, 1, 1, 1, 2, 3, 2, 3, 4, 1, 0, 1, 1, 3, 2, 1, 3, 1, 1, 3, 4, 4, 1, 3, 3, 0, 0, 4, 5, 3, 1, 2, 3, 0, 1, 4
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,2
|
|
COMMENTS
|
Conjecture: Let n be any nonnegative integer.
(i) Either a(n) > 0 or a(n-2) > 0. Also, a(n) > 0 or a(n-6) > 0. Moreover, if n has the form 2^k*(4m+1) with k and m nonnegative integers, then a(n) > 0 except for n = 813, 4404, 6420, 28804.
(ii) Either n or n-3 can be written as x^3 + y^2 + 3*z^2 with x,y,z nonnegative integers.
(iii) For each d = 4, 5, 11, 12, either n or n-d can be written as x^3 + y^2 + 2*z^2 with x,y,z nonnegative integers.
We have verified that a(n) or a(n-2) is positive for every n = 0..2*10^6. Note that for each n = 0,1,2,... either n or n-2 can be written as x^2 + y^2 + z^2 with x,y,z nonnegative integers, which follows immediately from the Gauss-Legendre theorem on sums of three squares.
|
|
LINKS
|
|
|
EXAMPLE
|
a(6) = 1 since 6 = 1^3 + 1^2 + 2^2.
a(14) = 1 since 14 = 1^3 + 2^2 + 3^2.
a(31) = 1 since 31 = 3^3 + 0^2 + 2^2.
|
|
MATHEMATICA
|
SQ[n_]:=SQ[n]=IntegerQ[Sqrt[n]]
Do[r=0; Do[If[SQ[n-x^3-y^2], r=r+1], {x, 0, n^(1/3)}, {y, 0, Sqrt[(n-x^3)/2]}]; Print[n, " ", r]; Continue, {n, 0, 80}]
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|