OFFSET
0,9
LINKS
Alois P. Heinz, Antidiagonals n = 0..140, flattened
FORMULA
G.f. of column k>0 satisfies: A_k(x) = 1+A_k(x)*(x-x^k*(1-A_k(x))), g.f. of column k=0: A_0(x) = 1/(1-x).
A(n,k) = A(n-1,k) + Sum_{j=1..n-k} A(j,k)*A(n-k-j,k) for n,k>0; A(n,0) = A(0,k) = 1.
G.f. of column k > 0: (1 - x + x^k - sqrt((1 - x + x^k)^2 - 4*x^k)) / (2*x^k). - Vaclav Kotesovec, Sep 02 2014
EXAMPLE
A(3,0) = 1: UDUDUD.
A(3,1) = 5: UDUDUD, UDUUDD, UUDDUD, UUDUDD, UUUDDD.
A(4,2) = 4: UDUDUDUD, UDUUUDDD, UUUDDDUD, UUUDUDDD.
A(5,2) = 8: UDUDUDUDUD, UDUDUUUDDD, UDUUUDDDUD, UDUUUDUDDD, UUUDDDUDUD, UUUDUDDDUD, UUUDUDUDDD, UUUUUDDDDD.
A(5,3) = 4: UDUDUDUDUD, UDUUUUDDDD, UUUUDDDDUD, UUUUDUDDDD.
Square array A(n,k) begins:
1, 1, 1, 1, 1, 1, 1, 1, ...
1, 1, 1, 1, 1, 1, 1, 1, ...
1, 2, 1, 1, 1, 1, 1, 1, ...
1, 5, 2, 1, 1, 1, 1, 1, ...
1, 14, 4, 2, 1, 1, 1, 1, ...
1, 42, 8, 4, 2, 1, 1, 1, ...
1, 132, 17, 7, 4, 2, 1, 1, ...
1, 429, 37, 12, 7, 4, 2, 1, ...
MAPLE
A:= proc(n, k) option remember;
`if`(k=0, 1, `if`(n=0, 1, A(n-1, k)
+add(A(j, k)*A(n-k-j, k), j=1..n-k)))
end:
seq(seq(A(n, d-n), n=0..d), d=0..15);
# second Maple program:
A:= (n, k)-> `if`(k=0, 1, coeff(series(RootOf(
A||k=1+A||k*(x-x^k*(1-A||k)), A||k), x, n+1), x, n)):
seq(seq(A(n, d-n), n=0..d), d=0..15);
MATHEMATICA
A[n_, k_] := A[n, k] = If[k == 0, 1, If[n == 0, 1, A[n-1, k] + Sum[A[j, k]*A[n-k-j, k], {j, 1, n-k}]]]; Table[Table[A[n, d-n], {n, 0, d}], {d, 0, 15}] // Flatten (* Jean-François Alcover, Jan 15 2014, translated from first Maple program *)
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
Alois P. Heinz, May 10 2012
STATUS
approved