OFFSET
2,2
REFERENCES
R. W. Robinson, personal communication.
R. W. Robinson, Numerical implementation of graph counting algorithms, AGRC Grant, Math. Dept., Univ. Newcastle, Australia, 1976.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
R. W. Robinson, Table of n, a(n) for n = 2..28
R. W. Robinson, Cubic labeled graphs, computer print-out, n.d. (see last page)
FORMULA
a(n) = (2*n)!*r(n)/(3*n*2^n) where r(2) = 1 and r(n) = (3*n-2) * (r(n-1) + Sum_{i=2..n-2} r(i) * r(n-i)). - Sean A. Irvine, Oct 11 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved