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%I #13 Aug 22 2017 20:53:12
%S 0,0,0,0,0,0,0,0,0,0,1,1,21,21,266,266,2646,2646,22827,22827,179487,
%T 179487,1323652,1323652,9321312,9321312,63436373,63436373,420693273,
%U 420693273,2734926558,2734926558,17505749898,17505749898,110687251039,110687251039
%N Number of palindromic structures using exactly six different symbols.
%C Permuting the symbols will not change the structure.
%D 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]
%H <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (1,20,-20,-155,155,580,-580,-1044,1044,720,-720).
%F a(n) = stirling2( [(n+1)/2], 6).
%F G.f.: x^11/((x-1)*(2*x-1)*(2*x+1)*(2*x^2-1)*(3*x^2-1)*(5*x^2-1)*(6*x^2-1)). [_Colin Barker_, Jul 24 2012]
%Y Cf. A000770, A056471.
%K nonn,easy
%O 1,13
%A _Marks R. Nester_
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