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A140426 Number of multi-symmetric Steinhaus matrices of size n.

%I A140426 #27 Sep 25 2019 07:47:37
%S A140426 1,1,2,1,2,2,2,2,4,2,4,4,4,4,8,4,8,8,8,8,16,8,16,16,16,16,32,16,32,32,
%T A140426 32,32,64,32,64,64,64,64,128,64,128,128,128,128,256,128,256,256,256,
%U A140426 256,512,256,512,512,512,512,1024,512,1024,1024,1024,1024,2048,1024,2048,2048,2048,2048,4096,2048
%N A140426 Number of multi-symmetric Steinhaus matrices of size n.
%C A140426 Theorem 3.7, p. 9, of Chappelon.
%H A140426 Jonathan Chappelon, <a href="http://arxiv.org/abs/0806.2779">Regular Steinhaus graphs of odd degree</a>, arXiv:0806.2779 [math.CO], 2008-2009.
%H A140426 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,0,2)
%F A140426 a(n) = 2^ceiling(n/6) for n even, 2^ceiling((n-3)/6) for n odd.
%F A140426 G.f.: ( -1-x-2*x^2-x^3-2*x^4-2*x^5 ) / ( -1+2*x^6 ). - _R. J. Mathar_, Jan 22 2011
%F A140426 a(n) = A060548(n-1) for n >= 2. - _Georg Fischer_, Nov 03 2018
%t A140426 LinearRecurrence[{0, 0, 0, 0, 0, 2}, {1, 1, 2, 1, 2, 2}, 100] (* _Jean-François Alcover_, Sep 25 2019 *)
%o A140426 (PARI) Vec((1 + x + 2*x^2 + x^3 + 2*x^4 + 2*x^5)/(1 - 2*x^6) + O(x^80)) \\ _Andrew Howroyd_, Nov 03 2018
%Y A140426 Cf. A060548.
%K A140426 easy,nonn
%O A140426 0,3
%A A140426 _Jonathan Vos Post_, Jun 18 2008