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 A219681 #6 Jul 23 2025 00:35:57 %S A219681 6,8,31,99,269,655,1506,3356,7278,15335,31362,62286,120292,226281, %T A219681 415250,744464,1305597,2242405,3775972,6240154,10130551,16171179, %U A219681 25404010,39307716,59953312,90205963,133984022,196588422,285117878,408987989 %N A219681 Number of nX3 arrays of the minimum value of corresponding elements and their horizontal, vertical or antidiagonal neighbors in a random, but sorted with lexicographically nondecreasing rows and nonincreasing columns, 0..2 nX3 array. %C A219681 Column 3 of A219686 %H A219681 R. H. Hardin, <a href="/A219681/b219681.txt">Table of n, a(n) for n = 1..210</a> %F A219681 Empirical: a(n) = (1/39916800)*n^11 - (1/3628800)*n^10 + (1/362880)*n^9 + (5/24192)*n^8 - (5639/1209600)*n^7 + (11267/172800)*n^6 - (26249/90720)*n^5 - (45251/36288)*n^4 + (5226461/226800)*n^3 - (303403/3150)*n^2 + (229729/1386)*n - 88 for n>4 %e A219681 Some solutions for n=3 %e A219681 ..0..0..0....2..1..1....0..0..0....1..0..0....1..0..0....1..0..0....0..0..0 %e A219681 ..0..0..0....2..1..1....0..0..0....1..0..0....0..0..0....1..0..0....0..0..0 %e A219681 ..2..1..1....2..1..1....1..1..1....1..1..2....0..0..2....2..0..0....2..0..0 %K A219681 nonn %O A219681 1,1 %A A219681 _R. H. Hardin_ Nov 25 2012