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A114293
Modified Schroeder numbers for q=5.
2
1, 1, 1, 1, 1, 1, 2, 2, 2, 1, 5, 5, 5, 2, 1, 13, 13, 13, 5, 2, 1, 42, 42, 42, 16, 6, 2, 1, 150, 150, 150, 57, 21, 6, 2, 1, 553, 553, 553, 210, 77, 21, 6, 2, 1, 2202, 2202, 2202, 836, 306, 82, 22, 6, 2, 1, 9233, 9233, 9233, 3505, 1282, 341, 89, 22, 6, 2, 1, 39726, 39726, 39726
OFFSET
0,7
COMMENTS
a(i,j) is the number of paths from (i,i) to (j,j) using steps of length (0,1), (1,0) and (1,1), not passing above the line y=x nor below the line y=2x/3. The Hamburger Theorem implies that we can use this table to calculate the number of domino tilings of an Aztec 5-pillow (A112836). To calculate this quantity, let P_n = the principal n X n submatrix of this array. If J_n = the back-diagonal matrix of order n, then A112836(n)=det(P_n+J_nP_n^(-1)J_n).
REFERENCES
C. Hanusa (2005). A Gessel-Viennot-Type Method for Cycle Systems with Applications to Aztec Pillows. PhD Thesis. University of Washington, Seattle, USA.
EXAMPLE
The number of paths from (0,0) to (4,4) staying between the lines y=x and y=2x/3 using steps of length (0,1), (1,0) and (1,1) is a(0,4)=5.
CROSSREFS
Sequence in context: A184242 A307739 A109978 * A295691 A285183 A255399
KEYWORD
nonn,tabl
AUTHOR
Christopher Hanusa (chanusa(AT)math.binghamton.edu), Nov 21 2005
STATUS
approved