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 A270543 #25 Sep 13 2023 17:04:13
%S A270543 1,3,11,13,25,27,39,41,57,59,71,73,93,95,107,109,129,131,147,149,169,
%T A270543 171,183,185,213,215,227,229,249,251,271,273,297,299,311,313,341,343,
%U A270543 355,357,385,387,407,409,429,431,443,445,481,483,499,501,521,523,543,545
%N A270543 Number of ordered pairs (i,j) of integers with |i|, |j| <= n, |i * j| <= n, and i even.
%F A270543 a(n) = 1 + 2*n + 2*floor(n/2) + 4*Sum_{k=1..floor(n/2)}floor(n/(2k)).
%F A270543 a(n) = A226355(n) - A270544(n).
%e A270543 a(0) = 1 from (i,j) = (0,0).
%e A270543 a(1) = 3 from (i,j) = (0,0), (0,1), (0,-1).
%e A270543 a(2) = 11: (0,0), (0,+-1), (0,+-2), (+-2, 0), (+-2,+-1).
%t A270543 a[n_]:=1+2n+2Floor[n/2]+4Sum[Floor[n/(2k)],{k,1,Floor[n/2]}]
%o A270543 (PARI) a(n) = {my(nb = 0); for (i=-n, n, if ((i % 2) == 0, for(j=-n, n, if (abs(i*j) <= n, nb++);););); nb;}
%Y A270543 The corresponding sequence where i is odd is A270544.
%Y A270543 Cf. A226355.
%K A270543 nonn
%O A270543 0,2
%A A270543 _Lorenz H. Menke, Jr._, Mar 18 2016
%E A270543 a(44) = 429 corrected by _Georg Fischer_, Sep 13 2023