cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-2 of 2 results.

A114297 First row of Modified Schroeder numbers for q=5 (A114293).

Original entry on oeis.org

1, 1, 1, 2, 5, 13, 42, 150, 553, 2202, 9233, 39726, 176932, 810798, 3786137, 18022100, 87265298, 428202617, 2127088358, 10684752474, 54181245592, 277101480826, 1428262595206, 7412626391101, 38712130945272, 203330779196084
Offset: 0

Views

Author

Christopher Hanusa (chanusa(AT)math.binghamton.edu), Nov 21 2005

Keywords

Comments

a(i) is the number of paths from (0,0) to (i,i) 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.

Examples

			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(4)=5.
		

References

  • C. Hanusa (2005). A Gessel-Viennot-Type Method for Cycle Systems with Applications to Aztec Pillows. PhD Thesis. University of Washington, Seattle, USA.

Crossrefs

A114292 Modified Schroeder numbers for q=3.

Original entry on oeis.org

1, 1, 1, 2, 2, 1, 5, 5, 2, 1, 16, 16, 6, 2, 1, 57, 57, 21, 6, 2, 1, 224, 224, 82, 22, 6, 2, 1, 934, 934, 341, 89, 22, 6, 2, 1, 4092, 4092, 1492, 384, 90, 22, 6, 2, 1, 18581, 18581, 6770, 1729, 393, 90, 22, 6, 2, 1, 86888, 86888, 31644, 8044, 1794, 394, 90, 22, 6, 2, 1
Offset: 0

Views

Author

Christopher Hanusa (chanusa(AT)math.binghamton.edu), Nov 21 2005

Keywords

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=x/2. The Hamburger Theorem implies that we can use this table to calculate the number of domino tilings of an Aztec 3-pillow (A112833). 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 A112833(n)=det(P_n+J_nP_n^(-1)J_n).

Examples

			The number of paths from (0,0) to (3,3) staying between the lines y=x and y=x/2 using steps of length (0,1), (1,0) and (1,1) is a(0,3)=5.
Triangle begins:
1;
1, 1;
2, 2, 1;
5, 5, 2, 1;
16, 16, 6, 2, 1;
57, 57, 21, 6, 2, 1;
224, 224, 82, 22, 6, 2, 1;
934, 934, 341, 89, 22, 6, 2, 1;
4092, 4092, 1492, 384, 90, 22, 6, 2, 1;
		

References

  • C. Hanusa (2005). A Gessel-Viennot-Type Method for Cycle Systems with Applications to Aztec Pillows. PhD Thesis. University of Washington, Seattle, USA.

Crossrefs

Programs

  • Maple
    b:= proc(x, y, k) option remember;
          `if`(y>x or y b(n, n, k):
    seq(seq(a(n,k), k=0..n), n=0..12); # Alois P. Heinz, Apr 26 2013
  • Mathematica
    b[x_, y_, k_] := b[x, y, k] = If[y>x || yJean-François Alcover, Mar 06 2015, after Alois P. Heinz *)
Showing 1-2 of 2 results.