

A318269


a(n) is the number of configurations of n indistinguishable pairs placed on the vertices of the ladder graph P_2 X P_n such that all but 4 such pairs are joined by an edge.


7



0, 0, 0, 0, 21, 347, 2919, 17050, 78815, 309075, 1072617, 3386970, 9921030, 27338000, 71614370, 179788174, 435311905, 1021684125, 2333955085, 5207067714, 11377225161, 24403026561, 51484962205, 107024887620, 219528748908, 444886466640, 891735024852, 1769575953980
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OFFSET

0,5


COMMENTS

This is also the number of "(n4)domino" configurations in the game of memory played on a 2 X n rectangular array, see [Young].  Donovan Young, Oct 23 2018


LINKS

Index entries for linear recurrences with constant coefficients, signature (9,31,44,4,84,66,46,74,4,36,4,9,1,1).


FORMULA

G.f.: x^2*(5*x^10 + 10*x^9 + 93*x^8 + 230*x^7 + 502*x^6 + 612*x^5 + 447*x^4 + 158*x^3 + 21*x^2)/(1  x)^4/(1  x  x^2)^5 (conjectured).


EXAMPLE



MATHEMATICA

CoefficientList[Normal[Series[x^2(5*x^10 + 10*x^9 + 93*x^8 + 230*x^7 + 502*x^6 + 612*x^5 + 447*x^4 + 158*x^3 + 21*x^2)/(1  x)^4/(1  x  x^2)^5, {x, 0, 30}]], x]


CROSSREFS



KEYWORD

nonn,easy


AUTHOR



EXTENSIONS



STATUS

approved



