OFFSET
1,3
COMMENTS
Wazir tours on a 4 X n grid. There are two closed loops for a 4x4 board, appearing as an H and a C, for example. - Ed Pegg Jr, Sep 07 2010
REFERENCES
F. Faase, On the number of specific spanning subgraphs of the graphs G X P_n, Ars Combin. 49 (1998), 129-154.
Kwong, Y. H. H.; Enumeration of Hamiltonian cycles in P_4 X P_n and P_5 X P_n. Ars Combin. 33 (1992), 87-96.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
Tosic R., Bodroza O., Harris Kwong Y. H. and Joseph Straight H., On the number of Hamiltonian cycles of P4 X Pn, Indian J. Pure Appl. Math. 21 (5) (1990), 403-409.
LINKS
F. Faase, On the number of specific spanning subgraphs of the graphs G X P_n, Preliminary version of paper that appeared in Ars Combin. 49 (1998), 129-154.
F. Faase, Results from the counting program
C. Flye Sainte-Marie, Manières différentes de tracer une route fermée ..., L'Intermédiaire des Mathématiciens, vol. 11 (1904), pp. 86-88 (in French).
George Jelliss, Wazir Wanderings
Index entries for linear recurrences with constant coefficients, signature (2, 2, -2, 1).
FORMULA
a(n) = 2*a(n-1) + 2*a(n-2) - 2*a(n-3) + a(n-4).
G.f.: x^2/(1-2x-2x^2+2x^3-x^4). - R. J. Mathar, Dec 16 2008
a(n)=sum ( sum ( binomial(k,j) * sum (binomial(j, i-j)*2^j *binomial(k-j,n-i-3*(k-j))*(-2)^(4*(k-j)-(n-i)), i,j,n-k+j) , j,0,k) , k,1,n ), n>0. - Vladimir Kruchinin, Aug 04 2010
a(n) = Sum_{k=1..n-1} A181688(k). - Kevin McShane, Aug 04 2019
PROG
(Maxima) a(n):=sum ( sum ( binomial(k, j) *sum (binomial(j, i-j)*2^j *binomial(k-j, n-i-3*(k-j))*(-2)^(4*(k-j)-(n-i)), i, j, n-k+j) , j, 0, k) , k, 1, n ); /* Vladimir Kruchinin, Aug 04 2010 */
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
STATUS
approved