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 A056473 Number of palindromic structures using exactly four different symbols. 1
 0, 0, 0, 0, 0, 0, 1, 1, 10, 10, 65, 65, 350, 350, 1701, 1701, 7770, 7770, 34105, 34105, 145750, 145750, 611501, 611501, 2532530, 2532530, 10391745, 10391745, 42355950, 42355950, 171798901 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,9 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 (1,9,-9,-26,26,24,-24). FORMULA stirling2( [(n+1)/2], 4). G.f.: x^7/((x-1)*(2*x-1)*(2*x+1)*(2*x^2-1)*(3*x^2-1)). [Colin Barker, Jul 24 2012] a(1)=a(2)=a(3)=a(4)=a(5)=a(6)=0, a(7)=1, a(n)=a(n-1)+9*a(n-2)-9*a(n-3)- 26*a(n-4)+ 26*a(n-5)+24*a(n-6)-24*a (n-7). - Harvey P. Dale, Mar 08 2013 MATHEMATICA StirlingS2[Floor[(Range[40]+1)/2], 4] (* or *) LinearRecurrence[ {1, 9, -9, -26, 26, 24, -24}, {0, 0, 0, 0, 0, 0, 1}, 40] (* Harvey P. Dale, Mar 08 2013 *) CROSSREFS Cf. A000453, A007581. Sequence in context: A270012 A219911 A056483 * A241869 A243126 A269921 Adjacent sequences:  A056470 A056471 A056472 * A056474 A056475 A056476 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified February 16 22:46 EST 2020. Contains 331976 sequences. (Running on oeis4.)