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 A187670 #6 Jul 22 2025 10:52:02 %S A187670 6,50,24,192,550,112,512,4044,11282,974,1126,17716,174292,612204,9928, %T A187670 2146,56080,1549398,36461174,65533922,197152,3760,150166,6839146, %U A187670 835707780 %N A187670 T(n,k)=Number of (n+1)X(n+1) 0..k arrays with each 2X2 subblock nonsingular and the array of 2X2 subblock determinants symmetric about the diagonal and antidiagonal. %C A187670 Table starts %C A187670 ......6.......50......192.......512....1126...2146.3760 %C A187670 .....24......550.....4044.....17716...56080.150166 %C A187670 ....112....11282...174292...1549398.6839146 %C A187670 ....974...612204.36461174.835707780 %C A187670 ...9928.65533922 %C A187670 .197152 %e A187670 Some k=3 solutions for 5X5 %e A187670 ..0..2..2..0..3....0..2..2..2..3....0..2..2..2..1....0..2..2..2..3 %e A187670 ..2..1..0..1..0....2..2..0..1..1....2..2..0..1..1....2..2..0..1..1 %e A187670 ..2..0..3..0..2....2..0..2..0..2....2..0..1..1..3....2..0..1..0..2 %e A187670 ..0..1..0..1..2....0..1..0..2..2....3..1..0..2..2....0..1..0..2..3 %e A187670 ..3..2..2..2..0....1..1..2..3..1....2..1..2..2..0....1..1..2..2..1 %Y A187670 Row 1 is A062801 %K A187670 nonn,tabl %O A187670 1,1 %A A187670 _R. H. Hardin_ Mar 12 2011