[Nauty-list] 8 seconds to canonize a 21-node graph

[Josh Jordan]

nauty 2.4 (32 bits) on an Athlon 64 takes over 8 seconds to canonize the
below 21-node digraph. Is this a bug? When I paste the input into dreadnaut,
it prints:

21 orbits; grpsize=1; 0 gens; 12004357 nodes (6220640 bad leaves); maxlev=14
tctotal=12004356; canupdates=160; cpu time = 8.27 seconds

nauty 2.2 takes about the same amount of time.

===== begin input to dreadnaut =======
-a+c+d-m
n=21
e
  0 :  1;
  1 :  2 3 4;
  2 :  3;
  3 :  4;
  4 :  2;
  5 :  6;
  7 :  2 8;
  9 :  10 12;
 10 :  11;
 12 :  14;
 13 :  3 14;
 15 :  16 18;
 16 :  17;
 18 :  20;
 19 :  20;
.
x
===== end input to dreadnaut =======
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