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A056471
Number of palindromic structures using a maximum of six different symbols.
5
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
1,3
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]
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]
CROSSREFS
Cf. A056452.
Sequence in context: A205482 A055879 A056470 * A164904 A188164 A245846
KEYWORD
nonn,easy
STATUS
approved