A181773 - OEIS

A181773

Molecular topological indices of the cocktail party graphs.

0, 48, 240, 672, 1440, 2640, 4368, 6720, 9792, 13680, 18480, 24288, 31200, 39312, 48720, 59520, 71808, 85680, 101232, 118560, 137760, 158928, 182160, 207552, 235200, 265200, 297648, 332640, 370272, 410640

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OFFSET

1,2

COMMENTS

a(n) is the number of 2 X 2 matrices (all four elements distinct) having entries in {-n,...,0,...,n} with determinant equal to the permanent. - Indranil Ghosh, Dec 25 2016

LINKS

Table of n, a(n) for n=1..30.

Eric Weisstein's World of Mathematics, Molecular Topological Index

Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1).

FORMULA

a(n) = 8*(n-1)*n*(2n-1).

a(n) = 16*A059270(n-1).

G.f.: 48*x^2*(x+1)/(x-1)^4. - Colin Barker, Oct 17 2012

a(n) = 48*A000330(n-1). - R. J. Mathar, Jan 04 2017

From Omar E. Pol, Jan 05 2017: (Start)

a(n) = 24*A006331(n-1) = 12*A002492(n-1) = 8*A055112(n-1).

a(n) = 2*A069074(n-2), n >= 2. (End)