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

1,8

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.

Links

Table of n, a(n) for n=1..16.

Formula

A000577(n) - A131481(n)

Crossrefs

Sequence in context: A355888 A203161 A050987 * A106269 A126758 A149258

Adjacent sequences: A137188 A137189 A137190 * A137192 A137193 A137194

Keyword

hard,more,nonn

Author

Tanya Khovanova, Mar 03 2008

Status

approved