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 A138778 #4 Dec 20 2014 18:35:36
%S A138778 1,4,10,20,35,56,2,84,14,120,56,165,168,220,420,286,924,3,364,1848,30,
%T A138778 455,3432,165,560,6006,660,680,10010,2145,816,16016,6006,4,969,24752,
%U A138778 15015,52,1140,37128,34320,364
%N A138778 Triangle read by rows: T(n,k)=k*binomial(n-2k,3k) (n>=5, 1<=k<=n/5).
%C A138778 Row n contains floor(n/5) terms.
%C A138778 Row sums yield A137359.
%D A138778 D. E. Knuth, The Art of Computer Programming, Vol. 4A, Section 7.1.4.
%p A138778 T:=proc(n,k) options operator, arrow: k*binomial(n-2*k,3*k) end proc: for n from 5 to 22 do seq(T(n,k),k=1..(1/5)*n) end do; # yields sequence in triangular form
%t A138778 Flatten[Table[k*Binomial[n-2k,3k],{n,5,30},{k,1,n/5}]] (* _Harvey P. Dale_, Dec 20 2014 *)
%Y A138778 Cf. A137359.
%K A138778 nonn,tabf
%O A138778 5,2
%A A138778 _Emeric Deutsch_, May 10 2008