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A172675 Number of 3*n X 3 0..2 arrays with row sums 2 and column sums 2*n. 1
21, 2385, 352128, 57775905, 10060071021, 1820016119376, 338183208699840, 64089909936535329, 12331175198408791725, 2401214665364782652385, 472159936393091112404160, 93594776429965445731933200 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Apparently the sequence gives the even-order terms in the diagonal of rational function R(x,y,z) = 1/(1 - (x^2 + y^2 + z^2 - x*y - y*z + x*z)), i.e., a(n) = [(x*y*z)^(2*n)] R(x,y,z), n >= 1. - Gheorghe Coserea, Aug 09 2018

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..33

CROSSREFS

Sequence in context: A033510 A123844 A172622 * A068254 A144853 A131314

Adjacent sequences:  A172672 A172673 A172674 * A172676 A172677 A172678

KEYWORD

nonn

AUTHOR

R. H. Hardin, Feb 06 2010

STATUS

approved

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Last modified April 22 04:04 EDT 2019. Contains 322329 sequences. (Running on oeis4.)