A032108 Number of reversible strings with n labeled beads of 3 colors.

3, 9, 81, 972, 14580, 262440, 5511240, 132269760, 3571283520, 107138505600, 3535570684800, 127280544652800, 4963941241459200, 208485532141286400, 9381848946357888000, 450328749425178624000

Offset: 1

Author

Christian G. Bower

Keywords

• nonn

Links

• C. G. Bower, Transforms (2)

Formula

"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).