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 A056421 #6 Aug 22 2017 20:53:11 %S A056421 4,6,16,45,72,404,456,2550,5144,26880,38568,367170,431776,3202964, %T A056421 8993712,33857520,63177816,636456776,803796696,6886253964,17456593904, %U A056421 79965511980,139069427016,1466861335900 %N A056421 Number of primitive (period n) step cyclic shifted sequences using a maximum of four different symbols. %C A056421 See A056371 for an explanation of step shifts. Under step cyclic shifts, abcde, bdace, bcdea, cdeab and daceb etc. are equivalent. %D A056421 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 A056421 Sum mu(d)*A056412(n/d) where d|n. %K A056421 nonn %O A056421 1,1 %A A056421 _Marks R. Nester_