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 A056420 #6 Aug 22 2017 20:53:11 %S A056420 3,3,7,15,21,79,75,306,433,1605,1695,12662,10461,57759,122791,347895, %T A056420 476049,3596917,3401967,22005312,41597289,142675887,186077883, %U A056420 1476684552,1694657979,8147271993,15690973311 %N A056420 Number of primitive (period n) step cyclic shifted sequences using a maximum of three different symbols. %C A056420 See A056371 for an explanation of step shifts. Under step cyclic shifts, abcde, bdace, bcdea, cdeab and daceb etc. are equivalent. %D A056420 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 A056420 Sum mu(d)*A056411(n/d) where d|n. %K A056420 nonn %O A056420 1,1 %A A056420 _Marks R. Nester_