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 A223920 #9 Jul 23 2025 04:39:06 %S A223920 10,100,666,3311,13347,45988,140236,387671,988447,2354539,5291652, %T A223920 11307388,23115717,45438234,86243127,158615577,283521156,493809754, %U A223920 839915122,1397838161,2280164963,3651068140,5746477482,8900889311 %N A223920 Number of 3Xn 0..2 arrays with rows and antidiagonals unimodal and columns nondecreasing. %C A223920 Row 3 of A223918 %H A223920 R. H. Hardin, <a href="/A223920/b223920.txt">Table of n, a(n) for n = 1..210</a> %F A223920 Empirical: a(n) = (1/19160064)*n^12 + (5/3193344)*n^11 + (1627/43545600)*n^10 + (257/483840)*n^9 + (2309/414720)*n^8 + (19319/483840)*n^7 + (8701321/43545600)*n^6 + (971137/1451520)*n^5 + (3369229/2177280)*n^4 + (294809/120960)*n^3 + (652717/237600)*n^2 + (521/385)*n + 1 %e A223920 Some solutions for n=3 %e A223920 ..0..0..1....0..1..0....0..1..1....2..0..0....1..0..0....0..0..1....0..1..1 %e A223920 ..2..1..1....1..1..1....1..1..2....2..2..1....1..2..0....0..1..2....1..1..1 %e A223920 ..2..2..1....1..2..2....1..2..2....2..2..2....1..2..2....1..1..2....1..1..2 %K A223920 nonn %O A223920 1,1 %A A223920 _R. H. Hardin_ Mar 29 2013