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 A223865 #6 Jul 23 2025 04:36:22 %S A223865 10,100,684,3526,14751,52591,165212,468292,1218812,2951732,6721028, %T A223865 14507390,29883426,59065484,112531519,207449471,371243434,646728936, %U A223865 1099377792,1827431562,2975775445,4754716769,7465089922,11531438986 %N A223865 Number of 2Xn 0..3 arrays with rows and antidiagonals unimodal and columns nondecreasing. %C A223865 Row 2 of A223864 %H A223865 R. H. Hardin, <a href="/A223865/b223865.txt">Table of n, a(n) for n = 1..210</a> %F A223865 Empirical: a(n) = (1/19160064)*n^12 + (1/456192)*n^11 + (2287/43545600)*n^10 + (215/290304)*n^9 + (3991/580608)*n^8 + (2369/53760)*n^7 + (8836141/43545600)*n^6 + (136571/207360)*n^5 + (654599/435456)*n^4 + (865283/362880)*n^3 + (289699/103950)*n^2 + (39143/27720)*n + 1 %e A223865 Some solutions for n=3 %e A223865 ..1..3..1....1..1..0....0..2..2....0..2..0....1..2..3....2..3..2....0..2..3 %e A223865 ..2..3..1....1..3..1....0..3..2....1..3..2....3..3..3....2..3..3....1..2..3 %K A223865 nonn %O A223865 1,1 %A A223865 _R. H. Hardin_ Mar 28 2013