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A137191 Number of n-celled polyiamonds with perimeter < n+2. 0
0, 0, 0, 0, 0, 1, 1, 4, 11, 39, 120, 403, 1254, 4000, 12475, 39030 (list; graph; refs; listen; history; text; internal format)
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

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Last modified September 27 22:01 EDT 2022. Contains 357063 sequences. (Running on oeis4.)