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A157518 Symmetric array T(n,m) of the number of 2-convex polygons with 2n horizontal and 2m vertical steps, read along diagonals. 0
6, 104, 104, 908, 1818, 908, 5298, 16560, 16560, 5298, 23261, 105510, 158768, 105510, 23261, 82603, 522325, 1086904, 1086904, 522325, 82603, 249245, 2125965, 5916957, 7962500, 5916957, 2125965, 249245, 661751, 7394811, 26917679 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

4,1

COMMENTS

The first rows and columns, n<4 or m<4, are all zero and omitted from the sequence. The type of analysis of the paper puts this in the OEIS category "walk."

LINKS

Table of n, a(n) for n=4..34.

W. R. G. James, I. Jensen, A. J. Guttmann, Exact generating function for 2-convex polygons, J. Phys A: Math. Theor. 41 (2008) 055001, eq (31).

Iwan Jensen, The anisotropic GF in Maple Friendly format.

EXAMPLE

The array starts at n=m=4 as

......6.....104.....908....5298...23261...82603..249245..661751.1585672

....104....1818...16560..105510..522325.2125965.7394811.22623747

....908...16560..158768.1086904.5916957.26917679.105571678

...5298..105510.1086904.7962500.46811313.232629941

..23261..522325.5916957.46811313.296064058

..82603.2125965.26917679.232629941

.249245.7394811.105571678

.661751.22623747

CROSSREFS

Sequence in context: A174481 A306205 A106303 * A001526 A295940 A106304

Adjacent sequences:  A157515 A157516 A157517 * A157519 A157520 A157521

KEYWORD

nonn,tabl

AUTHOR

R. J. Mathar, Mar 02 2009

STATUS

approved

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Last modified May 21 15:36 EDT 2022. Contains 353921 sequences. (Running on oeis4.)