%I #36 Feb 27 2020 11:47:19
%S 2,5,10,15,24,32,50
%N Maximal number of nodes in graph of degree <= n and diameter 2 (another version).
%C Comment from _Allan C. Wechsler_, Nov 22 2015: a(8) <= 65 by the Moore bound. Since 8 is not in {2,3,7,57}, we know a(8) <= 64. I don't know if we have any better upper bounds. This seems like a decent undergraduate research project. Pushing up the lower bound also.
%H F. Comellas, <a href="http://maite71.upc.es/grup_de_grafs/grafs/taula_delta_d.html">(Degree,Diameter) Problem for Graphs</a>
%H J. Dinneen, Michael; Hafner, Paul R., <a href="http://arxiv.org/abs/math/9504214">New Results for the Degree/Diameter Problem</a>, Networks 24 (1995), 359-367, arXiv:math/9504214 [math.CO], 1995.
%H Alan J. Hoffman, Robert R. Singleton, <a href="https://doi.org/10.1147/rd.45.0497">Moore graphs with diameter 2 and 3</a>, IBM Journal of Research and Development 5 (1960), 497-504.
%H Eyal Loz, Jozef Siran, <a href="https://ajc.maths.uq.edu.au/pdf/41/ajc_v41_p063.pdf">New record graphs in the degree-diameter problem</a>, Australasian Journal of Combinatorics 41 (1968), 63-80.
%H Brendan McKaya, Mirka Miller, Jozef Širáň, <a href="https://doi.org/10.1006/jctb.1998.1828">A note on large graphs of diameter two and given maximum degree</a>, Journal of Combinatorial Theory Series B 74 (1968): 110-118.
%H Mirka Miller, Jozef Sirán, <a href="http://www.combinatorics.org/ojs/index.php/eljc/article/view/DS14">Moore Graphs and Beyond: A survey of the Degree/Diameter Problem</a>, Electronic Journal of Combinatorics, Dynamic Survey DS14.
%H Guillermo Pineda-Villavicencio; José Gómez; Mirka Miller, Hebert Pérez-Rosés, <a href="https://doi.org/10.1016/j.endm.2006.06.044">New Largest Graphs of Diameter 6</a>, Electronic Notes in Discrete Mathematics 24 (2006), 153-160.
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Table_of_the_largest_known_graphs_of_a_given_diameter_and_maximal_degree">Table of the largest known graphs of a given diameter and maximal degree</a>
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Hoffman%E2%80%93Singleton_graph">Hoffman-Singleton Graph</a>
%e a(2) = 5 is achieved by the 5-cycle.
%e a(3) = 10 is achieved by the Petersen graph.
%K nonn,nice,hard,more
%O 1,1
%A _N. J. A. Sloane_, Oct 07 2001
%E It is known that a(8) >= 57.
%E Corrected and extended by _N. J. A. Sloane_, Nov 17 2015 following suggestions from _Allan C. Wechsler_ and _Christopher E. Thompson_.
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