A207640 Squares that can be written as a sum of 3 distinct nonzero squares in exactly two ways.

225, 361, 625, 900, 1444, 2500, 3600, 5776, 10000, 14400, 23104, 40000, 57600, 92416

Offset

1,1

Links

Table of n, a(n) for n=1..14.

Mathematica

t = Sort[Select[Flatten[Table[x^2 + y^2 + z^2, {x, 400}, {y, x + 1, 400}, {z, y + 1, 400}]], # < 160006 && IntegerQ[Sqrt[#]] &]];
f1[l_] := Module[{t = {}}, Do[If[l[[n]] != l[[n + 1]] && l[[n]] != l[[n - 1]], AppendTo[t, l[[n]]]], {n, Length[l] - 1}]; t];
f2[l_] := Module[{t = {}}, Do[If[l[[n]] == l[[n + 1]], AppendTo[t, l[[n]]]], {n, Length[l] - 1}]; t];
s1 = Join[{First[t]}, f1[t]];
Complement[t, s1];
t = f2[t];
s2 = Join[{First[t]}, f1[t]]

Crossrefs

Cf. A207638, A207639.

Sequence in context: A359598 A207639 A077347 * A267892 A363217 A373087

Adjacent sequences: A207637 A207638 A207639 * A207641 A207642 A207643

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Feb 19 2012

Status

approved