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 A274818 #23 Jul 10 2016 22:55:42 %S A274818 1,0,4,3,0,0,12,16,10,0,28,0,0,0 %N A274818 Triangle read by rows: T(n,k) = total number of regions in all arrangements of n circles in the affine plane forming k regions, including the regions that do not belong to the circles. %C A274818 Consider the arrangements of n circles described in A250001. %F A274818 T(n,k) = k*A274776(n,k). %e A274818 Triangle begins: %e A274818 1; %e A274818 0, 4, 3; %e A274818 0, 0, 12, 16, 10, 0, 28; %e A274818 0, 0, 0, ... %e A274818 ... %e A274818 For n = 3 and k = 5 there are 2 arrangements of 3 circles in the affine plane forming 5 regions, including the regions that do not belong to the circles, so T(3,5) = 2*5 = 10. %e A274818 For n = 3 and k = 6 there are no arrangements of 3 circles in the affine plane forming 6 regions, including the regions that do not belong to the circles, so T(3,6) = 0*5 = 0. %e A274818 Of course, there is a right triangle of all zeros starting from the second row. %Y A274818 Row sums give A274822. %Y A274818 First differs from A274819 at a(10). %Y A274818 Cf. A250001, A274776. %K A274818 nonn,tabf,hard,more %O A274818 1,3 %A A274818 _Omar E. Pol_, Jul 07 2016