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 A182406 #26 Feb 16 2025 08:33:13 %S A182406 1,0,2,0,2,3,0,2,18,4,0,2,246,84,5,0,2,7812,9612,260,6,0,2,580986, %T A182406 6000732,142820,630,7,0,2,101596896,20442892764,828850160,1166910, %U A182406 1302,8,0,2,41869995708,380053267505964,50820390410180,38128724910,6464682,2408,9 %N A182406 Square array A(n,k), n>=1, k>=1, read by antidiagonals: A(n,k) is the number of n-colorings of the square grid graph G_(k,k). %C A182406 The square grid graph G_(n,n) has n^2 = A000290(n) vertices and 2*n*(n-1) = A046092(n-1) edges. The chromatic polynomial of G_(n,n) has n^2+1 = A002522(n) coefficients. %H A182406 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/GridGraph.html">Grid Graph</a> %H A182406 Wikipedia, <a href="https://en.wikipedia.org/wiki/Chromatic_polynomial">Chromatic Polynomial</a> %e A182406 Square array A(n,k) begins: %e A182406 1, 0, 0, 0, 0, ... %e A182406 2, 2, 2, 2, 2, ... %e A182406 3, 18, 246, 7812, 580986, ... %e A182406 4, 84, 9612, 6000732, 20442892764, ... %e A182406 5, 260, 142820, 828850160, 50820390410180, ... %e A182406 6, 630, 1166910, 38128724910, 21977869327169310, ... %Y A182406 Columns k=1-7 give: A000027, A091940, A068239*2, A068240*2, A068241*2, A068242*2, A068243*2. %Y A182406 Rows n=1-20 give: A000007, A007395, A068253*3, A068254*4, A068255*5, A068256*6, A068257*7, A068258*8, A068259*9, A068260*10, A068261*11, A068262*12, A068263*13, A068264*14, A068265*15, A068266*16, A068267*17, A068268*18, A068269*19, A068270*20. %Y A182406 Cf. A182368. %K A182406 nonn,tabl %O A182406 1,3 %A A182406 _Alois P. Heinz_, Apr 27 2012