OFFSET
0,2
COMMENTS
a(1)..a(11) computed using software at http://users.cecs.anu.edu.au/~bdm/nauty/
REFERENCES
P. A. Morris, Letter to N. J. A. Sloane, Mar 02 1971.
LINKS
R. de Mello Koch, S. Ramgoolam, Strings from Feynman graph counting: Without large N, Phys. Rev. D 85 (2012) 026007
P. A. Morris, Letter to N. J. A. Sloane, Mar 02 1971.
R. C. Read, The enumeration of locally restricted graphs (I), J. London Math. Soc. 34 (1959) 417-436. - Jason Kimberley, Sep 17 2009
FORMULA
a(n)=N\{S_{2n}[S_3] * S_{3n}[S_2]\}. - Jason Kimberley, Sep 17 2009
PROG
(Sage)
h = SymmetricFunctions(QQ).homogeneous()
def A129427(n):
X = h([2*n]).plethysm(h([3]))
Y = h([3*n]).plethysm(h([2]))
return X.scalar(Y)
# Bruce Westbury, Aug 16 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Brendan McKay, Apr 15 2007
EXTENSIONS
Using equation (5.8) of Read 1959, new terms a(12) and a(13) were computed in MAGMA by Jason Kimberley, Sep 17 2009
Further terms a(14)-a(16) also computed by Jason Kimberley, announced Nov 09 2009
Formula corrected from n vertices to 2n vertices by Jason Kimberley, Nov 09 2009
Added a(0). - N. J. A. Sloane, Aug 26 2013
a(17)-a(19) from Sean A. Irvine, Oct 29 2016
STATUS
approved