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 A321840 #4 Nov 19 2018 18:03:21 %S A321840 24,60,210,609,1961,5952,19255,60812,200281,652011,2185981,7283988, %T A321840 24809651,84207955,290756694,1001820292,3500030779,12211804429, %U A321840 43101225586,151996648798,541273095677,1926487411495,6914504463171,24808989286716,89666142346093 %N A321840 Number of words w of length n such that each letter of the quaternary alphabet is used at least once and for every prefix z of w we have #(z,a_i) = 0 or #(z,a_i) >= #(z,a_j) for all j>i and #(z,a_i) counts the occurrences of the i-th letter in z. %H A321840 Alois P. Heinz, <a href="/A321840/b321840.txt">Table of n, a(n) for n = 4..150</a> %Y A321840 Column k=4 of A257783. %K A321840 nonn %O A321840 4,1 %A A321840 _Alois P. Heinz_, Nov 19 2018