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A131481
a(n) is the number of n-cell polyiamonds (triangular polyominoes) with perimeter n+2.
3
1, 1, 1, 3, 4, 11, 23, 62, 149, 409, 1066, 2931, 7981, 22166, 61508, 172267, 483088, 1361475, 3845139, 10894630
OFFSET
1,4
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)
CROSSREFS
a(n) <= A000577(n), a(n) <= A057729(n+2).
Sequence in context: A247171 A005218 A219514 * A001072 A292623 A077900
KEYWORD
nonn,hard,more
AUTHOR
Tanya Khovanova, Jul 27 2007
EXTENSIONS
Offset corrected and terms a(17)-a(20) added by John Mason, May 15 2021
STATUS
approved