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 A056279 #15 Apr 15 2021 16:38:57
%S A056279 0,0,1,6,25,89,301,960,3024,9305,28501,86430,261625,788669,2375075,
%T A056279 7140720,21457825,64435896,193448101,580597110,1742343323,5228050949,
%U A056279 15686335501,47063113320,141197991000,423610488665,1270865802276,3812663735790,11438127792025,34314649427035
%N A056279 Number of primitive (aperiodic) word structures of length n which contain exactly three different symbols.
%C A056279 Permuting the alphabet will not change a word structure. Thus aabc and bbca have the same structure.
%D A056279 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]
%H A056279 Andrew Howroyd, <a href="/A056279/b056279.txt">Table of n, a(n) for n = 1..500</a>
%F A056279 a(n) = Sum_{d|n} mu(d)*A000392(n/d) where n>0.
%F A056279 G.f.: Sum_{k>=1} mu(k) * x^(3*k) / Product_{j=1..3} (1 - j*x^k). - _Ilya Gutkovskiy_, Apr 15 2021
%Y A056279 Column 3 of A137651.
%Y A056279 Cf. A056268.
%K A056279 nonn
%O A056279 1,4
%A A056279 _Marks R. Nester_
%E A056279 Terms a(26) and beyond from _Andrew Howroyd_, Apr 15 2021