can anybody extend this new sequence?

[Jeremy Gardiner]

Please can anybody extend this new sequence?

My poor old BASIC interpreter hasn't found a(5) after 48 hours of running
...

%I A000001
%S A000001 0,7,640,170555,
%N A000001 a(n) = number of labeled 3-regular (trivalent) multi-graphs
without loops on 2n vertices with a maximum of 2 edges between any pair of
nodes.

Also a(n) = number of labeled symmetric 2nx2n matrices with {0,1,2}-entries
with row sum equal to 3 for each row and trace 0.
%e A000001 a(2)=7 because for 2*n=4 nodes there are 7 possible labelled
graphs whose adjacency matrices are as follows:

0 2 1 0
2 0 0 1
1 0 0 2
0 1 2 0

0 1 2 0
1 0 0 2
2 0 0 1
0 2 1 0

0 2 0 1
2 0 1 0
0 1 0 2
1 0 2 0

0 1 1 1
1 0 1 1
1 1 0 1
1 1 1 0

0 0 2 1
0 0 1 2
2 1 0 0
1 2 0 0

0 1 0 2
1 0 2 0
0 2 0 1
2 0 1 0

0 0 1 2
0 0 2 1
1 2 0 0
2 1 0 0
%Y A000001 Cf. A001205, A002829, A108243.
%O A000001 1
%K A000001 ,more,nonn,
%A A000001 Jeremy Gardiner (jeremy.gardiner at btinternet.com), Aug 29 2005