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 A056269 #7 Aug 22 2017 20:53:07 %S A056269 0,0,0,24,240,1560,8400,40800,186480,818280,3498000,14674440,60780720, %T A056269 249393480,1016542560,4123132800,16664094960,67171179600,270232006800, %U A056269 1085569963080,4356217672800,17466683473800 %N A056269 Number of primitive (aperiodic) words of length n which contain exactly four different symbols. %D A056269 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 A056269 sum mu(d)*A000919(n/d) where d|n. %F A056269 Seems to be n * A056289. %Y A056269 Cf. A000302, A000919, A054719. %K A056269 nonn %O A056269 1,4 %A A056269 _Marks R. Nester_