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 A210541 #13 Jul 22 2025 22:30:40
%S A210541 1,1,1,1,2,4,8,16,33,73,177,467,1309,3813,11409,34999,110510,361194,
%T A210541 1226930,4334048,15877297,60049447,233426007,929616461,3786970033,
%U A210541 15777120457,67260334185,293617319221,1312868943154,6010792180952
%N A210541 Number of arrays of n nonnegative integers with value i>0 appearing only after i-1 has appeared at least 4 times.
%C A210541 Column 4 of A210545
%H A210541 R. H. Hardin, <a href="/A210541/b210541.txt">Table of n, a(n) for n = 1..210</a>
%H A210541 Rigoberto Flórez, José L. Ramírez, Fabio A. Velandia, and Diego Villamizar, <a href="https://arxiv.org/abs/2308.02059">Some Connections Between Restricted Dyck Paths, Polyominoes, and Non-Crossing Partitions</a>, arXiv:2308.02059 [math.CO], 2023. See Table 1 p. 13.
%F A210541 a(n) = 1 if n<=4 else sum{i=0..n-4}(binomial(n-4,i)*a(i)). Proved by _R. J. Mathar_ in the Sequence Fans Mailing List.
%e A210541 Some solutions for n=13
%e A210541 ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
%e A210541 ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
%e A210541 ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
%e A210541 ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
%e A210541 ..1....1....1....0....1....1....1....0....1....1....0....0....1....0....0....1
%e A210541 ..1....1....1....1....1....0....1....0....1....1....1....1....0....1....1....1
%e A210541 ..0....1....0....0....1....0....1....0....0....0....0....1....0....0....1....0
%e A210541 ..0....1....1....1....1....1....0....1....1....1....1....0....1....1....1....1
%e A210541 ..1....2....1....0....0....1....1....1....1....1....0....0....1....1....1....0
%e A210541 ..1....0....2....1....2....1....0....0....2....0....0....0....0....1....0....0
%e A210541 ..0....1....1....1....2....2....1....1....1....0....0....1....0....2....2....1
%e A210541 ..1....0....2....0....1....2....1....1....0....1....0....1....1....0....1....1
%e A210541 ..2....0....1....2....1....0....2....2....2....0....0....1....2....0....2....0
%K A210541 nonn
%O A210541 1,5
%A A210541 _R. H. Hardin_, Mar 22 2012