A057170 - OEIS

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A057170

2-enumeration of 2n X 2n half-turn symmetric alternating-sign matrices.

1, 2, 12, 288, 26880, 10035200, 14836039680, 87734404251648, 2064716402685640704, 194361783607326689722368, 72958995691997968023051829248, 109548594452892660460226753134067712, 656593430123179564638165745256190909087744, 15741504841171021653720624575980053578961033101312 (list; graph; refs; listen; history; internal format)

	OFFSET	`0,2`
	LINKS	`G. Kuperberg, Symmetry classes of alternating-sign matrices under one roof, arXiv math.CO/0008184 [Th. 3]`
	MAPLE	`A057170 := proc(n) local i, j, t1; t1 := 2^(n^2); for i to n do for j to n do if j-i mod 2 <> 0 then t1 := t1(2j - 2i + 1)/(2j - 2*i) end if end do end do; t1 end proc;`
	CROSSREFS	`Sequence in context: A083568 A003121 A176037 * A200564 A008338 A000178` `Adjacent sequences: A057167 A057168 A057169 * A057171 A057172 A057173`
	KEYWORD	`nonn,easy`
	AUTHOR	`N. J. A. Sloane (njas(AT)research.att.com), Feb 04 2001`

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Last modified February 14 23:53 EST 2012. Contains 205689 sequences.