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 A049735 #14 Aug 07 2021 04:15:10
%S A049735 1,5,5,13,9,13,29,21,21,29,49,37,25,37,49,81,57,45,45,57,81,113,89,69,
%T A049735 61,69,89,113,149,121,97,81,81,97,121,149,197,161,129,109,101,109,129,
%U A049735 161,197,253,213,177,145,137,137,145,177,213,253
%N A049735 Array T(i,j) is the number of lattice points (x,y) in circle with radius (0,0)-to-(i,j), read by antidiagonals.
%C A049735 Specifically, x^2 + y^2 <= i^2 + j^2.
%F A049735 T(n,0) = A000328(n).
%e A049735 Antidiagonals (each starting on row 0):
%e A049735 {1},
%e A049735 {5, 5},
%e A049735 {13, 9, 13},
%e A049735 ...
%e A049735 Array begins:
%e A049735 1 5 13 29 49 81
%e A049735 5 9 21 37 57 89
%e A049735 13 21 25 45 69 97
%e A049735 29 37 45 61 81 109
%e A049735 49 57 69 81 101 137
%e A049735 81 89 97 109 137 161
%o A049735 (PARI) T(n, k) = my(z=norml2([n, k]), m=ceil(sqrt(2)*max(n,k))); sum(x=-m, m, sum(y=-m, m, norml2([x, y]) <= z)); \\ _Michel Marcus_, Aug 07 2021
%Y A049735 Cf. A000328 (1st column or row).
%K A049735 nonn,tabl
%O A049735 0,2
%A A049735 _Clark Kimberling_