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A032108
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Number of reversible strings with n labeled beads of 3 colors.
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0
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3, 9, 81, 972, 14580, 262440, 5511240, 132269760, 3571283520, 107138505600, 3535570684800, 127280544652800, 4963941241459200, 208485532141286400, 9381848946357888000, 450328749425178624000
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OFFSET
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1,1
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LINKS
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FORMULA
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"BIJ" (reversible, indistinct, labeled) transform of 3, 0, 0, 0...
3^n*n!/2 (n>1). E.g.f.: (2-9*x^2)/(2-6*x).
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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