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 A223866 #6 Jul 23 2025 04:36:28 %S A223866 20,400,4884,41682,273959,1477240,6818350,27746619,101698292, %T A223866 341120712,1060013078,3081189588,8443340635,21952389700,54443494785, %U A223866 129382581759,295772387822,652604111790,1393875593290,2889329636208,5825806879833 %N A223866 Number of 3Xn 0..3 arrays with rows and antidiagonals unimodal and columns nondecreasing. %C A223866 Row 3 of A223864 %H A223866 R. H. Hardin, <a href="/A223866/b223866.txt">Table of n, a(n) for n = 1..210</a> %F A223866 Empirical: a(n) = (1/3629463552000)*n^18 + (7/403273728000)*n^17 + (667/951035904000)*n^16 + (3281/174356582400)*n^15 + (148069/402361344000)*n^14 + (1366301/249080832000)*n^13 + (3748907/57480192000)*n^12 + (1190879/1916006400)*n^11 + (344761547/73156608000)*n^10 + (684241027/24385536000)*n^9 + (104051693257/804722688000)*n^8 + (54794329/119750400)*n^7 + (786440609/628992000)*n^6 + (81330893999/31135104000)*n^5 + (895703793151/217945728000)*n^4 + (8582457311/1816214400)*n^3 + (317136049/79168320)*n^2 + (10267897/6126120)*n + 1 %e A223866 Some solutions for n=3 %e A223866 ..0..1..2....0..1..0....3..2..0....0..0..0....0..0..0....0..2..0....0..0..0 %e A223866 ..2..2..2....0..3..0....3..2..0....1..3..1....3..1..0....0..2..0....1..1..0 %e A223866 ..2..3..3....1..3..2....3..3..0....3..3..2....3..3..1....1..3..1....3..3..1 %K A223866 nonn %O A223866 1,1 %A A223866 _R. H. Hardin_ Mar 28 2013