This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A056475 #13 Aug 22 2017 20:53:12 %S A056475 0,0,0,0,0,0,0,0,0,0,1,1,21,21,266,266,2646,2646,22827,22827,179487, %T A056475 179487,1323652,1323652,9321312,9321312,63436373,63436373,420693273, %U A056475 420693273,2734926558,2734926558,17505749898,17505749898,110687251039,110687251039 %N A056475 Number of palindromic structures using exactly six different symbols. %C A056475 Permuting the symbols will not change the structure. %D A056475 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 A056475 <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 A056475 a(n) = stirling2( [(n+1)/2], 6). %F A056475 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 A056475 Cf. A000770, A056471. %K A056475 nonn,easy %O A056475 1,13 %A A056475 _Marks R. Nester_