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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 (list; graph; refs; listen; history; text; internal format)
 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] LINKS Index entries for linear recurrences with constant coefficients, signature (1,15,-15,-80,80,180,-180,-144,144). 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 Adjacent sequences:  A056468 A056469 A056470 * A056472 A056473 A056474 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified October 15 12:31 EDT 2019. Contains 328026 sequences. (Running on oeis4.)