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A059475 Number of 2n X 2n half-turn symmetric alternating-sign matrices (HTSASM's). 5
1, 2, 10, 140, 5544, 622908, 198846076, 180473355920, 465904151957920, 3422048076740462480, 71525763221287897903500, 4254840960508487045451825000, 720428791920558617462950575000000, 347230535542092373572967034254050000000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

REFERENCES

Paul Barry, Jacobsthal Decompositions of Pascal's Triangle, Ternary Trees, and Alternating Sign Matrices, Journal of Integer Sequences, 19, 2016, #16.3.5.

LINKS

Table of n, a(n) for n=0..13.

J. de Gier, Loops, matchings and alternating-sign matrices

Heuer, Dylan, Chelsey Morrow, Ben Noteboom, Sara Solhjem, Jessica Striker, and Corey Vorland. "Chained permutations and alternating sign matrices - Inspired by three-person chess." Discrete Mathematics 340, no. 12 (2017): 2732-2752. Also arXiv:1611.03387.

G. Kuperberg, Symmetry classes of alternating-sign matrices under one roof, arXiv math.CO/0008184

FORMULA

A005130(n)*A006366(n).

CROSSREFS

Even-numbered terms of A005158.

Sequence in context: A213955 A091990 A014228 * A156296 A003046 A294115

Adjacent sequences:  A059472 A059473 A059474 * A059476 A059477 A059478

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Feb 04 2001

STATUS

approved

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Last modified February 23 21:23 EST 2018. Contains 299588 sequences. (Running on oeis4.)