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R. W. Robinson, <a href="/A007099/b007099_1.txt">Table of n, a(n) for n = 1..29</a> (corrected by Michel Marcus, Jan 19 2019)
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R. W. Robinson, <a href="/A007099/b007099_1.txt">Table of n, a(n) for n = 21..29</a> (corrected by Michel Marcus, Jan 19 2019)
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G.-B. Chae, E. M. Palmer, R. W. Robinson, <a href="http://dx.doi.org/10.1016/j.disc.2007.03.011">Counting labeled general cubic graphs</a>, Discr. Math. 307 (2007) 2979-2992, eqs. (23) and (24).
s := proc(n)
option remember;
if n = 1 then
0;
elif n = 2 then
1;
else
3*n*procname(n-1)+2*procname(n-2)+(3*n-1)*add(procname(i)*procname(n-1-i), i=2..n-3) ;
end if;
end proc:
A007099 := proc(n)
if n = 1 then
0;
elif n = 2 then
1;
else
(2*n)!/3/n/2^n*(s(n)-2*s(n-1)) ;
end if;
end proc: # R. J. Mathar, Nov 08 2018
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