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 A056393 #10 Aug 22 2017 20:53:10
%S A056393 1,2,4,11,17,107,131,811,1893,11107,17599,179371,233449,1866057,
%T A056393 5603787,22469291,44744047,477262537,636308685,5732457131,15272176697,
%U A056393 73301054891,133274359129,1466413263531
%N A056393 Number of step shifted (decimated) sequence structures using a maximum of four different symbols.
%C A056393 See A056371 for an explanation of step shifts. Permuting the symbols will not change the structure.
%D A056393 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]
%F A056393 Use de Bruijn's generalization of Polya's enumeration theorem as discussed in reference.
%F A056393 a(n) = Sum_{k=1..4} A288620(n, k). - _Andrew Howroyd_, Jun 13 2017
%Y A056393 Cf. A056373, A288620.
%K A056393 nonn
%O A056393 1,2
%A A056393 _Marks R. Nester_