A131893 a(n) is the number of shapes of balanced trees with constant branching factor 7 and n nodes. The node is balanced if the size, measured in nodes, of each pair of its children differ by at most one node.

1, 7, 21, 35, 35, 21, 7, 1, 49, 1029, 12005, 84035, 352947, 823543, 823543, 17294403, 155649627, 778248135, 2334744405, 4202539929, 4202539929, 1801088541, 21012699645, 105063498225, 291843050625, 486405084375, 486405084375