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A001926 G.f.: (1+x)^2/[(1-x)^4(1-x-x^2)^3].
(Formerly M4628 N1978)
2
1, 9, 46, 177, 571, 1632, 4270, 10446, 24244, 53942, 115954, 242240, 494087, 987503, 1939634, 3753007, 7167461, 13532608, 25293964, 46856332, 86110792, 157125052, 284866900, 513470464, 920659517, 1642844485, 2918680214, 5164483453, 9104522495, 15995633440 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

From rook polynomials.

REFERENCES

J. Riordan, Discordant permutations, Scripta Math., 20 (1954), 14-23.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

T. D. Noe, Table of n, a(n) for n = 0..1000

Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992.

Simon Plouffe, 1031 Generating Functions and Conjectures, Université du Québec à Montréal, 1992.

J. Riordan, Discordant permutations, Scripta Math., 20 (1954), 14-23. [Annotated scanned copy]

MAPLE

A001926:=-(1+z)**2/(z**2+z-1)**3/(z-1)**4; [Conjectured (correctly) by Simon Plouffe in his 1992 dissertation.]

MATHEMATICA

nn = 30; CoefficientList[Series[(1 + x)^2/((1 - x)^4 (1 - x - x^2)^3), {x, 0, nn}], x] (* T. D. Noe, Aug 17 2012 *)

CROSSREFS

Second differences are in A002941.

Sequence in context: A201458 A034487 A035039 * A213749 A085385 A217152

Adjacent sequences:  A001923 A001924 A001925 * A001927 A001928 A001929

KEYWORD

nonn

AUTHOR

N. J. A. Sloane.

EXTENSIONS

Edited by N. J. A. Sloane, Apr 10 2009

STATUS

approved

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Last modified November 19 02:01 EST 2018. Contains 317332 sequences. (Running on oeis4.)