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 A239927 #36 Mar 11 2015 10:58:57
%S A239927 1,0,1,0,0,1,0,0,0,1,0,0,1,0,1,0,0,0,2,0,1,0,0,0,0,3,0,1,0,0,0,1,0,4,
%T A239927 0,1,0,0,0,0,3,0,5,0,1,0,0,0,1,0,6,0,6,0,1,0,0,0,0,3,0,10,0,7,0,1,0,0,
%U A239927 0,0,0,7,0,15,0,8,0,1,0,0,0,0,2,0,14,0,21,0,9,0,1,0,0,0,0,0,7,0,25,0,28,0,10,0,1,0,0,0,0,1,0,17,0,41,0,36,0,11,0,1
%N A239927 Triangle read by rows: T(n,k) is the number of Dyck paths of semilength k such that the area between the x-axis and the path is n (n>=0; 0<=k<=n).
%C A239927 Triangle A129182 transposed.
%C A239927 Column sums give the Catalan numbers (A000108).
%C A239927 Row sums give A143951.
%C A239927 Sums along falling diagonals give A005169.
%C A239927 T(4n,2n) = A240008(n). - _Alois P. Heinz_, Mar 30 2014
%H A239927 Joerg Arndt and Alois P. Heinz, <a href="/A239927/b239927.txt">Rows n = 0..140, flattened</a>
%F A239927 G.f.: F(x,y) satisfies F(x,y) = 1 / (1 - x*y * F(x, x^2*y) ).
%F A239927 G.f.: 1/(1 - y*x/(1 - y*x^3/(1 - y*x^5/(1 - y*x^7/(1 - y*x^9/( ... )))))).
%e A239927 Triangle begins:
%e A239927 00: 1;
%e A239927 01: 0, 1;
%e A239927 02: 0, 0, 1;
%e A239927 03: 0, 0, 0, 1;
%e A239927 04: 0, 0, 1, 0, 1;
%e A239927 05: 0, 0, 0, 2, 0, 1;
%e A239927 06: 0, 0, 0, 0, 3, 0, 1;
%e A239927 07: 0, 0, 0, 1, 0, 4, 0, 1;
%e A239927 08: 0, 0, 0, 0, 3, 0, 5, 0, 1;
%e A239927 09: 0, 0, 0, 1, 0, 6, 0, 6, 0, 1;
%e A239927 10: 0, 0, 0, 0, 3, 0, 10, 0, 7, 0, 1;
%e A239927 11: 0, 0, 0, 0, 0, 7, 0, 15, 0, 8, 0, 1;
%e A239927 12: 0, 0, 0, 0, 2, 0, 14, 0, 21, 0, 9, 0, 1;
%e A239927 13: 0, 0, 0, 0, 0, 7, 0, 25, 0, 28, 0, 10, 0, 1;
%e A239927 14: 0, 0, 0, 0, 1, 0, 17, 0, 41, 0, 36, 0, 11, 0, 1;
%e A239927 15: 0, 0, 0, 0, 0, 5, 0, 35, 0, 63, 0, 45, 0, 12, 0, 1;
%e A239927 16: 0, 0, 0, 0, 1, 0, 16, 0, 65, 0, 92, 0, 55, 0, 13, 0, 1;
%e A239927 17: 0, 0, 0, 0, 0, 5, 0, 40, 0, 112, 0, 129, 0, 66, 0, 14, 0, 1;
%e A239927 18: 0, 0, 0, 0, 0, 0, 16, 0, 86, 0, 182, 0, 175, 0, 78, 0, 15, 0, 1;
%e A239927 19: 0, 0, 0, 0, 0, 3, 0, 43, 0, 167, 0, 282, 0, 231, 0, 91, 0, 16, 0, 1;
%e A239927 20: 0, 0, 0, 0, 0, 0, 14, 0, 102, 0, 301, 0, 420, 0, 298, 0, 105, 0, 17, 0, 1;
%e A239927 ...
%e A239927 Column k=4 corresponds to the following 14 paths (dots denote zeros):
%e A239927 #: path area steps (Dyck word)
%e A239927 01: [ . 1 . 1 . 1 . 1 . ] 4 + - + - + - + -
%e A239927 02: [ . 1 . 1 . 1 2 1 . ] 6 + - + - + + - -
%e A239927 03: [ . 1 . 1 2 1 . 1 . ] 6 + - + + - - + -
%e A239927 04: [ . 1 . 1 2 1 2 1 . ] 8 + - + + - + - -
%e A239927 05: [ . 1 . 1 2 3 2 1 . ] 10 + - + + + - - -
%e A239927 06: [ . 1 2 1 . 1 . 1 . ] 6 + + - - + - + -
%e A239927 07: [ . 1 2 1 . 1 2 1 . ] 8 + + - - + + - -
%e A239927 08: [ . 1 2 1 2 1 . 1 . ] 8 + + - + - - + -
%e A239927 09: [ . 1 2 1 2 1 2 1 . ] 10 + + - + - + - -
%e A239927 10: [ . 1 2 1 2 3 2 1 . ] 12 + + - + + - - -
%e A239927 11: [ . 1 2 3 2 1 . 1 . ] 10 + + + - - - + -
%e A239927 12: [ . 1 2 3 2 1 2 1 . ] 12 + + + - - + - -
%e A239927 13: [ . 1 2 3 2 3 2 1 . ] 14 + + + - + - - -
%e A239927 14: [ . 1 2 3 4 3 2 1 . ] 16 + + + + - - - -
%e A239927 There are no paths with weight < 4, one with weight 4, none with weight 5, 3 with weight 6, etc., therefore column k=4 is
%e A239927 [0, 0, 0, 0, 1, 0, 3, 0, 3, 0, 3, 0, 2, 0, 1, 0, 1, 0, 0, 0, ...].
%e A239927 Row n=8 is [0, 0, 0, 0, 3, 0, 5, 0, 1], the corresponding paths of weight=8 are:
%e A239927 Semilength 4:
%e A239927 [ . 1 . 1 2 1 2 1 . ]
%e A239927 [ . 1 2 1 . 1 2 1 . ]
%e A239927 [ . 1 2 1 2 1 . 1 . ]
%e A239927 Semilength 6:
%e A239927 [ . 1 . 1 . 1 . 1 . 1 2 1 . ]
%e A239927 [ . 1 . 1 . 1 . 1 2 1 . 1 . ]
%e A239927 [ . 1 . 1 . 1 2 1 . 1 . 1 . ]
%e A239927 [ . 1 . 1 2 1 . 1 . 1 . 1 . ]
%e A239927 [ . 1 2 1 . 1 . 1 . 1 . 1 . ]
%e A239927 Semilength 8:
%e A239927 [ . 1 . 1 . 1 . 1 . 1 . 1 . 1 . 1 . ]
%p A239927 b:= proc(x, y, k) option remember;
%p A239927 `if`(y<0 or y>x or k<0, 0, `if`(x=0, `if`(k=0, 1, 0),
%p A239927 b(x-1, y-1, k-y+1/2)+ b(x-1, y+1, k-y-1/2)))
%p A239927 end:
%p A239927 T:= (n, k)-> b(2*k, 0, n):
%p A239927 seq(seq(T(n, k), k=0..n), n=0..20); # _Alois P. Heinz_, Mar 29 2014
%t A239927 b[x_, y_, k_] := b[x, y, k] = If[y<0 || y>x || k<0, 0, If[x == 0, If[k == 0, 1, 0], b[x-1, y-1, k-y+1/2] + b[x-1, y+1, k-y-1/2]]]; T[n_, k_] := b[2*k, 0, n]; Table[ Table[T[n, k], {k, 0, n}], {n, 0, 20}] // Flatten (* _Jean-François Alcover_, Feb 18 2015, after _Alois P. Heinz_ *)
%o A239927 (PARI)
%o A239927 rvec(V) = { V=Vec(V); my(n=#V); vector(n, j, V[n+1-j] ); }
%o A239927 print_triangle(V)= { my( N=#V ); for(n=1, N, print( rvec( V[n]) ) ); }
%o A239927 N=20; x='x+O('x^N);
%o A239927 F(x,y, d=0)=if (d>N, 1, 1 / (1-x*y * F(x, x^2*y, d+1) ) );
%o A239927 v= Vec( F(x,y) );
%o A239927 print_triangle(v)
%Y A239927 Sequences obtained by particular choices for x and y in the g.f. F(x,y) are: A000108 (F(1, x)), A143951 (F(x, 1)), A005169 (F(sqrt(x), sqrt(x))), A227310 (1+x*F(x, x^2), also 2-1/F(x, 1)), A239928 (F(x^2, x)), A052709 (x*F(1,x+x^2)), A125305 (F(1, x+x^3)), A002212 (F(1, x/(1-x))).
%Y A239927 Cf. A047998, A138158, A227543.
%Y A239927 Cf. A129181.
%K A239927 nonn,tabl
%O A239927 0,19
%A A239927 _Joerg Arndt_, Mar 29 2014