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 A138777 #4 Mar 07 2013 19:33:25
%S A138777 1,3,6,10,15,21,1,28,6,36,21,45,56,55,126,66,252,1,78,462,9,91,792,45,
%T A138777 105,1287,165,120,2002,495,136,3003,1287,1,153,4368,3003,12,171,6188,
%U A138777 6435,78,190,8568,12870,364
%N A138777 Triangle read by rows: T(n,k)=binomial(n-2k,3k+2) (n>=2, 0<=k<=(n-2)/5).
%C A138777 Row n contains floor((n+3)/5) terms.
%C A138777 Row sums yield A137358.
%D A138777 D. E. Knuth, The Art of Computer Programming, Vol. 4A, Section 7.1.4.
%p A138777 T:=proc(n,k) options operator, arrow: binomial(n-2*k,3*k+2) end proc: for n from 2 to 20 do seq(T(n,k),k=0..(n-2)*1/5) end do; # yields sequence in triangular form
%t A138777 Flatten[Table[Binomial[n-2k,3k+2],{n,2,20},{k,0,(n-2)/5}]] (* _Harvey P. Dale_, Mar 07 2013 *)
%Y A138777 Cf. A137358.
%K A138777 nonn,tabf
%O A138777 2,2
%A A138777 _Emeric Deutsch_, May 10 2008