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Search: id:A141147
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| A141147 |
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Number of linear arrangements of n blue, n red and n green items such that the first item is blue and there are no adjacent items of the same color (first and last elements considered as adjacent). |
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+0
3
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| 2, 8, 44, 268, 1732, 11624, 80096, 562748, 4013396, 28964128, 211054120, 1550226880, 11463513440, 85257846080, 637243586944, 4783617720892, 36046416801268, 272543202174704, 2066898899119448, 15717398604230888
(list; graph; listen)
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OFFSET
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1,1
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LINKS
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L. Q. Eifler, K. B. Reid Jr., D. P. Roselle, Sequences with adjacent elements unequal, Aequationes Mathematicae 6 (2-3), 1971.
Max Alekseyev, PARI scripts for various problems
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FORMULA
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a(n) = A110707(n) / 3
a(n) = Sum[k=0..[n/2]] binomial(n,2k) * binomial(2k,k) * binomial(n-1+k,k) * 2^(n-2k)
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PROGRAM
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(PARI) { a(n) = sum(k=0, n\2, binomial(n, 2*k) * binomial(2*k, k) * binomial(n-1+k, k) * 2^(n-2*k) ) }
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CROSSREFS
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Cf. A110706, A110707, A110710, A110711, A141146, A141148.
Sequence in context: A047851 A121747 A014508 this_sequence A120928 A111537 A051045
Adjacent sequences: A141144 A141145 A141146 this_sequence A141148 A141149 A141150
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KEYWORD
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nonn
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AUTHOR
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Max Alekseyev (maxale(AT)gmail.com), Jun 10 2008
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