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 A056439 #6 Aug 22 2017 20:53:11 %S A056439 1,1,1,2,2,5,4,10,9,22,14,78,36,124,180,343,260,1329,804,3732,4428, %T A056439 9742,8384,47364,33778,108292,138756,408244,331184,2251604,1155734 %N A056439 Number of primitive (period n) step cyclic shifted sequence structures using a maximum of two different symbols. %C A056439 See A056371 for an explanation of step shifts. Under step cyclic shifts, abcde, bdace, bcdea, cdeab and daceb etc. are equivalent. Permuting the symbols will not change the structure. %D A056439 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 A056439 Sum mu(d)*A056429(n/d) where d divides n. %Y A056439 Cf. A002730. %K A056439 nonn %O A056439 1,4 %A A056439 _Marks R. Nester_