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A097203 Number of 4-tuples (a,b,c,d) with 1 <= a <= b <= c <= d, a^2+b^2+c^2+d^2 = n and gcd(a,b,c,d) = 1. 4
0, 0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 2, 0, 1, 2, 0, 1, 2, 1, 1, 2, 1, 2, 0, 0, 3, 2, 1, 2, 1, 2, 0, 2, 2, 1, 3, 1, 2, 3, 0, 2, 4, 1, 2, 2, 1, 3, 0, 1, 3, 3, 2, 2, 4, 2, 0, 3, 2, 3, 3, 2, 3, 3, 0, 2, 5, 2, 3, 3, 2, 4, 0, 1, 5, 4, 2, 4, 2, 3, 0, 4, 4, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,28

COMMENTS

The old entry with this sequence number was a duplicate of A034836.

From Wolfdieter Lang, Mar 25 2013: (Start)

a(n) = 0 if n has no partition with four parts, each a (nonzero) square, and the parts have no common factor > 1.

n is not representable as a primitive sum of four nonzero squares.

If n' has a representation [s(1),s(2),s(3),s(4)] with 1 <= s(1) <= s(2) <= s(3) <= s(4) and sum(s(j)^2,j=1..4) = n', then [k*s(1),k*s(2),k*s(3),k*s(4)] is a representation of n := k^2*n'. Therefore, only primitive representations with gcd(s(1),s(2),s(3),s(4)) = 1 are here considered.

See A025428(n) for the multiplicity of the representations of n as a sum of four nonzero squares.

For the n values with a(n) not zero (primitively representable as a sum of four nonzero squares) see A222949. (End)

LINKS

N. J. A. Sloane, Vinay Vaishampayan and Alois P. Heinz, Table of n, a(n) for n = 1..10000 (terms n = 1..1024 from N. J. A. Sloane and Vinay Vaishampayan)

FORMULA

If a(n) > 0 then 8 does not divide n.

a(n) = k if there are k different quadruples [s(1),s(2),s(3),s(4)] with 1 <= s(1) <= s(2) <= s(3) <= s(4), gcd(s(1),s(2),s(3),s(4)) = 1 and sum(s(j)^2,j=1..4) = n. If there is no such quadruple then a(n) = 0. - Wolfdieter Lang, Mar 25 2013

EXAMPLE

The solutions (if any) for n <= 20 are as follows:

n = 1:

n = 2:

n = 3:

n = 4: 1 1 1 1

n = 5:

n = 6:

n = 7: 1 1 1 2

n = 8:

n = 9:

n = 10: 1 1 2 2

n = 11:

n = 12: 1 1 1 3

n = 13: 1 2 2 2

n = 14:

n = 15: 1 1 2 3

n = 16:

n = 17:

n = 18: 1 2 2 3

n = 19: 1 1 1 4

n = 20: 1 1 3 3

From Wolfdieter Lang, Mar 25 2013: (Start)

a(16) = 0 because 16 is not a primitive sum of four nonzero squares. The representation [2,2,2,2] of 16 is not primitive.

a(40) = 0 because the only representation as sum of four nonzero squares (A025428(4) = 1) is [2,2,4,4], but this is not primitive.

a(28) = 2 because the two primitive representations of 28 are

[1, 1, 1, 5] and [1, 3, 3, 3]. [2, 2, 2, 4] = 2*[1, 1, 1, 2] is not primitive due to 28 = 2^2*7. (End)

MAPLE

b:= proc(n, i, g, t) option remember; `if`(n=0,

      `if`(g=1 and t=0, 1, 0), `if`(i<1 or t=0 or i^2*t<n, 0,

       b(n, i-1, g, t)+ `if`(i^2>n, 0, b(n-i^2, i, igcd(g, i), t-1))))

    end:

a:= n-> `if`(n<4, 0, b(n, isqrt(n-3), 0, 4)):

seq(a(n), n=1..120);  # Alois P. Heinz, Apr 02 2013

MATHEMATICA

Clear[b]; b[n_, i_, g_, t_] := b[n, i, g, t] = If[n == 0, If[g == 1 && t == 0, 1, 0], If[i < 1 || t == 0 || i^2*t < n, 0, b[n, i-1, g, t] + If[i^2 > n, 0, b[n-i^2, i, GCD[g, i], t-1]]]]; a[n_] := If[n < 4, 0, b[n, Sqrt[n-3] // Floor, 0, 4]]; Table[a[n], {n, 1, 99}] (* Jean-Fran├žois Alcover, Apr 05 2013, translated from Alois P. Heinz's Maple program *)

CROSSREFS

Cf. A025428, A000414, A222949.

Sequence in context: A194519 A025855 A215590 * A025850 A096771 A129714

Adjacent sequences:  A097200 A097201 A097202 * A097204 A097205 A097206

KEYWORD

nonn

AUTHOR

N. J. A. Sloane and Vinay Vaishampayan, Oct 22 2008

STATUS

approved

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Last modified August 9 07:42 EDT 2022. Contains 356019 sequences. (Running on oeis4.)