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 A056281 #16 Apr 15 2021 21:40:42
%S A056281 0,0,0,0,1,15,140,1050,6951,42524,246730,1379385,7508501,40074895,
%T A056281 210766919,1096189500,5652751651,28958088579,147589284710,
%U A056281 749206047975,3791262568261,19137821665325,96416888184100
%N A056281 Number of primitive (aperiodic) word structures of length n which contain exactly five different symbols.
%C A056281 Permuting the alphabet will not change a word structure. Thus aabc and bbca have the same structure.
%D A056281 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 A056281 a(n) = Sum_{n > 0, d|n} mu(d)*A000481(n/d).
%F A056281 G.f.: Sum_{k>=1} mu(k) * x^(5*k) / Product_{j=1..5} (1 - j*x^k). - _Ilya Gutkovskiy_, Apr 15 2021
%Y A056281 Column 5 of A137651.
%Y A056281 Cf. A056270.
%K A056281 nonn
%O A056281 1,6
%A A056281 _Marks R. Nester_