Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #9 Jun 23 2024 11:51:39
%S 0,0,0,0,0,0,1,1,3,3,4,5,9,9,14
%N Number of trees with n nodes which have nodes that cannot be gracefully labeled '0'.
%C Also called non-0-ubiquitous.
%H Frank Van Bussel, <a href="https://doi.org/10.1016/S0012-365X(03)00152-3">0-Centred and 0-ubiquitously graceful trees</a>, Discrete Mathematics 277.1-3 (2004): 193-218. See Section 2.
%e For n=6 the tree with a-b-c-d-e
%e \
%e f
%e has no graceful solution with 'c' labeled as '0'.
%K nonn,more
%O 0,9
%A _Michael Arnold_, Jun 15 2024