A131481 - OEIS

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A131481

a(n) is the number of n-cell polyiamonds (triangular polyominoes) with perimeter n+2.

1, 1, 1, 3, 4, 11, 23, 62, 149, 409, 1066, 2931, 7981, 22166, 61508, 172267 (list; graph; refs; listen; history; internal format)

	OFFSET	`0,4`
	COMMENTS	`n+2 is the maximal perimeter for an n-celled polyiamond. a(n) is the number of n-celled polyiamonds that have a tree as their connectedness graph (vertices of this graph correspond to cells and two vertices are connected if the corresponding cells have a common edge)`
	LINKS	`Isoperimetrical Polyiamonds` `Poly Pages`
	CROSSREFS	`a(n) <= A000577(n), a(n) <= A057729(n+2).` `Sequence in context: A001642 A001643 A005218 * A001072 A077900 A198443` `Adjacent sequences: A131478 A131479 A131480 * A131482 A131483 A131484`
	KEYWORD	`hard,more,nonn`
	AUTHOR	`Tanya Khovanova (tanyakh(AT)yahoo.com), Jul 27 2007`

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Last modified February 15 04:23 EST 2012. Contains 205694 sequences.