Degree-diameter problem $N(20,4)$

The largest possible number of vertices in a graph of maximum degree $20$ and diameter $4$.

Updates

• 2010-09 Lower bound: $34952$ (34,952)
  Loz, E., & Pineda-Villavicencio, G. (2010). New benchmarks for large-scale networks with given maximum degree and diameter. The Computer Journal, 53(7), 1092-1105.
  [via The Degree Diameter Problem for General Graphs - Combinatorics Wiki]