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 A259600 #12 Jul 31 2015 04:28:35
%S A259600 4,5,7,7,9,10,9,11,12,14,10,12,13,15,17,12,14,15,17,19,20,13,15,16,18,
%T A259600 20,21,23,15,17,18,20,22,23,25,26,17,19,20,22,24,25,27,28,30,18,20,21,
%U A259600 23,25,26,28,29,31,33,20,22,23,25,27,28,30,31,33,35,36
%N A259600 Triangular array: sums of two distinct lower Wythoff numbers.
%C A259600 Row n shows the numbers u(m) + u(n), where u = A000201 (lower Wythoff sequence), for m=1..n-1, for n >= 2. (The offset is 2, so that the top row is counted as row 2.)
%e A259600 10 = 4 + 6 = u(3) + u(4), so that 10 appears as the final term in row 4. (The offset is 2, so that the top row is counted as row 2.) Rows 2 to 9:
%e A259600 4
%e A259600 5 7
%e A259600 7 9 10
%e A259600 9 11 12 14
%e A259600 10 12 13 15 17
%e A259600 12 14 15 17 19 20
%e A259600 13 15 16 18 20 21 23
%e A259600 15 17 18 20 22 23 25 26
%t A259600 r = GoldenRatio; z = 20; u[n_] := u[n] = Floor[n*r];
%t A259600 s[m_, n_] := u[m] + u[n]; t = Table[s[m, n], {n, 2, z}, {m, 1, n - 1}];
%t A259600 TableForm[t] (* A259600 array *)
%t A259600 Flatten[t] (* A259600 sequence *)
%o A259600 (PARI) tabl(nn) = {r=(sqrt(5)+1)/2; for (n=2, nn, for (k=1, n-1, print1(floor(n*r) + floor(k*r), ", ");); print(););} \\ _Michel Marcus_, Jul 30 2015
%Y A259600 Cf. A259556, A259601.
%K A259600 nonn,tabl,easy
%O A259600 2,1
%A A259600 _Clark Kimberling_, Jul 22 2015