0,4

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)

Isoperimetrical Polyiamonds

Poly Pages

a(n) <= A000577(n), a(n) <= A057729(n+2).

Sequence in context: A001642 A001643 A005218 this_sequence A001072 A077900 A041231

Adjacent sequences: A131478 A131479 A131480 this_sequence A131482 A131483 A131484

hard,more,nonn

Tanya Khovanova (tanyakh(AT)yahoo.com), Jul 27 2007