A056471 Number of palindromic structures using a maximum of six different symbols.

1, 1, 2, 2, 5, 5, 15, 15, 52, 52, 203, 203, 876, 876, 4111, 4111, 20648, 20648, 109299, 109299, 601492, 601492, 3403127, 3403127, 19628064, 19628064, 114700315, 114700315, 676207628, 676207628, 4010090463

Offset: 1

Author

Marks R. Nester

Keywords

• nonn
• easy

Comments

Permuting the symbols will not change the structure.

References

• M. R. Nester (1999). Mathematical investigations of some plant interaction designs. PhD Thesis. University of Queensland, Brisbane, Australia. [See A056391 for pdf file of Chap. 2]

Links

• Index entries for linear recurrences with constant coefficients, signature (1,15,-15,-80,80,180,-180,-144,144).

Crossrefs

Cf. A056452.

Formula

Sum stirling2( [(n+1)/2], k) for k from 1 to 6.

G.f.: -x*(91*x^8-135*x^6+68*x^4-14*x^2+1) / ((x-1)*(2*x-1)*(2*x+1)*(2*x^2-1)*(3*x^2-1)*(6*x^2-1)). [Colin Barker, Dec 05 2012]