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%I #7 Mar 30 2012 17:37:01
%S 3,9,81,972,14580,262440,5511240,132269760,3571283520,107138505600,
%T 3535570684800,127280544652800,4963941241459200,208485532141286400,
%U 9381848946357888000,450328749425178624000
%N Number of reversible strings with n labeled beads of 3 colors.
%H C. G. Bower, <a href="/transforms2.html">Transforms (2)</a>
%F "BIJ" (reversible, indistinct, labeled) transform of 3, 0, 0, 0...
%F 3^n*n!/2 (n>1). E.g.f.: (2-9*x^2)/(2-6*x).
%K nonn
%O 1,1
%A _Christian G. Bower_
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