id:A128565 - OEIS Search Results

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Column 1 of triangle A128564; a(n) equals the number of permutations of {1..n+2} with [n/2+1] inversions for n>=0.

+0
3

1, 2, 5, 9, 29, 49, 174, 285, 1068, 1717, 6655, 10569, 41926, 66013, 266338, 416687, 1703027, 2651355, 10947079, 16976806, 70673825, 109256095, 457927079, 706071989, 2976282415, 4579020513, 19395654894, 29784426945, 126688273871 (list; graph; listen)

	OFFSET	`0,2`
	FORMULA	`a(n) = A008302(n+2,[n/2+1]) = coefficient of q^[n/2+1] in the q-factorial of n+2 for n>=0.`
	PROGRAM	`(PARI) {a(n)=polcoeff(prod(j=1, n+2, (1-q^j)/(1-q)), (n+2)\2, q)}`
	CROSSREFS	`Cf. A008302 (Mahonian numbers); A128564 (triangle), A128566 (column 2).` `Sequence in context: A139796 A086586 A105456 this_sequence A090291 A109469 A083460` `Adjacent sequences: A128562 A128563 A128564 this_sequence A128566 A128567 A128568`
	KEYWORD	`nonn`
	AUTHOR	`Paul D. Hanna (pauldhanna(AT)juno.com), Mar 12 2007`

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Last modified September 5 19:27 EDT 2008. Contains 143485 sequences.

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