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 A056426 #6 Aug 22 2017 20:53:11 %S A056426 0,0,0,3,12,136,204,1434,3520,20688,31956,317374,390364,2973332, %T A056426 8504708,32469954,61276740,622084744,790198476,6798276744,17290257884, %U A056426 79394924652,138325216092,1460955163540 %N A056426 Number of primitive (period n) step cyclic shifted sequences using exactly four different symbols. %C A056426 See A056371 for an explanation of step shifts. Under step cyclic shifts, abcde, bdace, bcdea, cdeab and daceb etc. are equivalent. %D A056426 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 A056426 Sum mu(d)*A056417(n/d) where d|n. %Y A056426 Cf. A056421. %K A056426 nonn %O A056426 1,4 %A A056426 _Marks R. Nester_