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%I #13 May 15 2021 13:20:36
%S 1,1,1,3,4,11,23,62,149,409,1066,2931,7981,22166,61508,172267,483088,
%T 1361475,3845139,10894630
%N a(n) is the number of n-cell polyiamonds (triangular polyominoes) with perimeter n+2.
%C 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)
%H Andrew Clarke, <a href="http://www.recmath.com/PolyPages/PolyPages/index.htm?Isopoly1s.html">Isoperimetrical Polyiamonds</a>
%Y a(n) <= A000577(n), a(n) <= A057729(n+2).
%K nonn,hard,more
%O 1,4
%A _Tanya Khovanova_, Jul 27 2007
%E Offset corrected and terms a(17)-a(20) added by _John Mason_, May 15 2021
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