0,3

See A210000 for a guide to related sequences.

Chai Wah Wu, Table of n, a(n) for n = 0..1000

a(2)=5 counts these matrices:

2 0...2 1...2 0...2 0...2 2

0 2...0 2...1 2...2 2...0 2

a = 0; b = n; z1 = 20;

t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]]

c[n_, k_] := c[n, k] = Count[t[n], k]

c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, 0, m}]

Table[c1[n, n^2] - c1[n, 2 n - 1], {n, 0, z1}]

Cf. A210000.

Sequence in context: A145013 A096943 A166810 * A261347 A079909 A301518

Adjacent sequences: A210364 A210365 A210366 * A210368 A210369 A210370

nonn

Clark Kimberling, Mar 20 2012

approved