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 A138775 #4 Oct 14 2012 17:35:26
%S A138775 1,1,1,1,1,1,1,1,4,1,10,1,20,1,35,1,56,1,1,84,7,1,120,28,1,165,84,1,
%T A138775 220,210,1,286,462,1,1,364,924,10,1,455,1716,55,1,560,3003,220,1,680,
%U A138775 5005,715,1,816,8008,2002,1
%N A138775 Triangle read by rows: T(n,k)=binomial(n-2k,3k) (n>=0, 0<=k<=n/5).
%C A138775 Row n contains 1+floor(n/5) terms.
%C A138775 Row sums yield A137356.
%D A138775 D. E. Knuth, The Art of Computer Programming, Vol. 4A, Section 7.1.4.
%p A138775 T:=proc(n,k) options operator, arrow: binomial(n-2*k, 3*k) end proc: for n from 0 to 20 do seq(T(n,k),k=0..(1/5)*n) end do; # yields sequence in triangular form
%t A138775 Flatten[Table[Binomial[n-2k,3k],{n,0,20},{k,0,Floor[n/5]}]] (* _Harvey P. Dale_, Oct 14 2012 *)
%Y A138775 Cf. A137356.
%K A138775 nonn,tabf
%O A138775 0,9
%A A138775 _Emeric Deutsch_, May 10 2008