A137191 Number of n-celled polyiamonds with perimeter < n+2.

0, 0, 0, 0, 0, 1, 1, 4, 11, 39, 120, 403, 1254, 4000, 12475, 39030

Offset: 1

Author

Tanya Khovanova, Mar 03 2008

Keywords

• hard
• more
• nonn

Comments

These are n-cell polyiamonds with the perimeter less than the maximum possible one.

If we associate a graph to a polyiamond with vertices representing cells and edges representing two cells with a common edge, then this sequence enumerates polyiamonds whose corresponding graphs have cycles.

Formula

A000577(n) - A131481(n)