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 A049649 #19 Aug 06 2021 17:31:21
%S A049649 1,1,4,5,7,8,11,14,17,18,23,28,31,34,41,46,51,54,61,70,75,78,89,100,
%T A049649 105,110,123,130,137,144,153,168,177,182,199,216,223,230,249,260,269,
%U A049649 278,291,312,323,330,353,372,381,392,413,430,443,454,473,500,513,520,549,578,587,602
%N A049649 T(n,n+3), array T given by A049639.
%H A049649 Sean A. Irvine, <a href="/A049649/b049649.txt">Table of n, a(n) for n = 0..500</a> (terms 1..76 from G. C. Greubel)
%t A049649 T[0 | 1, 0 | 1] = 0; T[0 | 1, _] = T[_, 0 | 1] = 1; T[i_, j_] := Module[{slopes, cnt}, slopes = Union@Flatten@Table[(k - j)/(h - i), {h, 0, i - 1}, {k, 0, j - 1}]; cnt[slope_] := Count[Flatten[Table[{h, k}, {h, 0, i - 1}, {k, 0, j - 1}], 1], {h_, k_} /; (k - j)/(h - i) == slope]; Count[cnt /@ slopes, c_ /; c >= 2] + 2]; Table[T[n, n + 3], {n, 0, 50}] (* _G. C. Greubel_, Dec 05 2017 *)
%Y A049649 Cf. A049639.
%K A049649 nonn
%O A049649 0,3
%A A049649 _Clark Kimberling_
%E A049649 Terms a(37) onward added by _G. C. Greubel_, Dec 10 2017
%E A049649 Missing a(0)=1 inserted by _Sean A. Irvine_, Aug 06 2021