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 A224004 #6 Jul 23 2025 04:49:44 %S A224004 729,20216,117386,388598,984595,2160036,4368458,8412641,15703623, %T A224004 28693082,51589943,91524689,160402902,277798382,475383309,803588211, %U A224004 1341439640,2210851797,3597065144,5777447600,9161521721,14345876103 %N A224004 Number of 6Xn 0..2 arrays with antidiagonals unimodal and rows and diagonals nondecreasing. %C A224004 Row 6 of A223999 %H A224004 R. H. Hardin, <a href="/A224004/b224004.txt">Table of n, a(n) for n = 1..210</a> %F A224004 Empirical: a(n) = (1/3628800)*n^12 + (1/302400)*n^11 + (419/3628800)*n^10 + (223/120960)*n^9 + (35411/1209600)*n^8 + (20443/50400)*n^7 + (17616857/3628800)*n^6 + (6342323/120960)*n^5 + (821276033/1814400)*n^4 + (103253527/37800)*n^3 + (186412339/16800)*n^2 - (24901729/840)*n - 64275 for n>8 %e A224004 Some solutions for n=3 %e A224004 ..0..1..1....0..0..0....0..0..0....0..0..2....0..0..0....0..0..0....0..0..2 %e A224004 ..0..1..2....0..0..2....0..2..2....1..1..2....0..2..2....0..0..0....0..1..1 %e A224004 ..0..0..1....0..0..0....0..1..2....1..1..2....1..2..2....0..0..1....1..1..1 %e A224004 ..0..2..2....0..0..0....1..1..1....0..1..1....0..1..2....1..1..2....0..2..2 %e A224004 ..1..1..2....0..0..2....0..1..1....0..1..2....0..1..1....1..1..1....1..1..2 %e A224004 ..1..1..2....1..1..2....2..2..2....1..2..2....0..2..2....0..1..2....0..1..2 %K A224004 nonn %O A224004 1,1 %A A224004 _R. H. Hardin_ Mar 30 2013