3,1

Column 4 of triangle A234350.

Without the restriction "non-equivalent (mod D_3)" the numbers are given by A194132.

Table of n, a(n) for n=3..17.

There are a(3) = 2 non-equivalent ways to arrange 4 indistinguishable points (x) on a triangular grid of side 3:

x .

x x x x

. x . x . x

Cf. A234350, A194132

Arranging 3 points: A234351

Arranging 5 points: A234353

Arranging 6 points: A234354

Sequence in context: A163752 A035600 A189247 * A241623 A288443 A108476

Adjacent sequences: A234349 A234350 A234351 * A234353 A234354 A234355

nonn,more

Heinrich Ludwig, Dec 30 2013

a(14)-a(17) from Heinrich Ludwig, Apr 19 2016

approved