A234351 Number of non-equivalent (mod D_3) ways to arrange 3 indistinguishable points on a triangular grid of side n so that no three points are collinear.

1, 5, 22, 77, 217, 530, 1149, 2288, 4231, 7400, 12322, 19725, 30486, 45768, 66917, 95669

Offset

2,2

Comments

Column 3 of triangle A234350.

Without the restriction "non-equivalent (mod D_3)" the numbers are given by A194131.

Links

Table of n, a(n) for n=2..17.

Example

There are a(3) = 5 non-equivalent ways to arrange 3 indistinguishable points (x) on a triangular grid of side 3:
     x         .         x         x         x
    . .       x x       x x       . .       x .
   x . x     . x .     . . .     . x x     . x .

Crossrefs

Cf. A234350, A194131

Arranging 4 points: A234352

Arranging 5 points: A234353

Arranging 6 points: A234354

Sequence in context: A338707 A058750 A058752 * A255802 A266358 A183925

Adjacent sequences: A234348 A234349 A234350 * A234352 A234353 A234354

Keyword

nonn,more

Author

Heinrich Ludwig, Dec 30 2013

Extensions

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

Status

approved