OFFSET
5,3
COMMENTS
This sequence, S_n in Guy's 1958 paper, counts triangulations of a regular n-gon into n-2 triangles such that the only symmetries of the triangulation are the identity and a single reflection ("symmetry of a kite"). Triangulations related by a symmetry of the underlying n-gon do not count as distinct. - Joseph Myers, Jun 21 2012
A000108 is a subsequence, see formula. - Ralf Stephan, Aug 19 2004 (edited, Joerg Arndt, Aug 31 2014)
REFERENCES
R. K. Guy, Dissecting a polygon into triangles, Bull. Malayan Math. Soc., Vol. 5, pp. 57-60, 1958.
R. K. Guy, Dissecting a polygon into triangles, Research Paper #9, Math. Dept., Univ. Calgary, 1967.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Joseph Myers, Table of n, a(n) for n = 5..1000
S. J. Cyvin, J. Brunvoll, E. Brendsdal, B. N. Cyvin and E. K. Lloyd, Enumeration of polyene hydrocarbons: a complete mathematical solution, J. Chem. Inf. Comput. Sci., 35 (1995) 743-751.
S. J. Cyvin, J. Brunvoll, E. Brendsdal, B. N. Cyvin and E. K. Lloyd, Enumeration of polyene hydrocarbons: a complete mathematical solution, J. Chem. Inf. Comput. Sci., 35 (1995) 743-751. [Annotated scanned copy]
R. K. Guy, Dissecting a polygon into triangles, Research Paper #9, Math. Dept., Univ. Calgary, 1967. [Annotated scanned copy]
FORMULA
a(2n+3) = A000108(n), n>0. - M. F. Hasler, Mar 25 2012
a(n) = Catalan(floor(n/2) - 1) - Catalan(n/4 - 1) - Catalan (n/6 - 1), where Catalan(x) = 0 for noninteger x (from Guy's 1958 paper). - Joseph Myers, Jun 21 2012
MATHEMATICA
c[n_Integer] := CatalanNumber[n]; c[_] = 0; a[n_] := c[Floor[n/2]-1] - c[n/4-1] - c[n/6-1]; Array[a, 40, 5] (* Jean-François Alcover, Feb 03 2016, after Joseph Myers *)
PROG
(PARI)
C(n)=if(type(n)==type(1), binomial(2*n, n)/(n+1), 0);
a(n)=C(floor(n/2)-1) - C(n/4-1) - C(n/6-1);
vector(66, n, a(n+4))
\\ Joerg Arndt, Aug 31 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Extended by Joseph Myers, Jun 21 2012
STATUS
approved