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 A056424 #10 Aug 22 2017 20:53:11 %S A056424 0,1,2,3,4,8,8,18,18,38,28,142,72,234,360,669,520,2606,1608,7338,8856, %T A056424 19370,16768,94308,67556,216200,277512,815310,662368,4499852,2311468, %U A056424 8465496,13045076,31592762,40937592,159769394,103197488,401912086 %N A056424 Number of primitive (period n) step cyclic shifted sequences using exactly two different symbols. %C A056424 Identical to A002730 for n>1. %C A056424 See A056371 for an explanation of step shifts. Under step cyclic shifts, abcde, bdace, bcdea, cdeab and daceb etc. are equivalent. %D A056424 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 A056424 a(n) = sum( d divides n, mu(d) * A056415(n/d) ). %Y A056424 Cf. A002730. %K A056424 nonn %O A056424 1,3 %A A056424 _Marks R. Nester_ %E A056424 Added more terms (from A002730), _Joerg Arndt_, Aug 27 2014