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A135331
Triangle read by rows: T(n,k) is the number of Dyck paths of semilength n having k DUUU's starting at level 1.
1
1, 1, 2, 5, 13, 1, 36, 6, 105, 27, 320, 108, 1, 1011, 409, 10, 3289, 1508, 65, 10957, 5491, 347, 1, 37216, 19898, 1658, 14, 128435, 72063, 7395, 119, 449142, 261436, 31527, 794, 1, 1588228, 951258, 130353, 4583, 18
OFFSET
0,3
COMMENTS
The formula for T(n,k)=l_{n,k} in the reference (p. 2919) does not appear to work (a typo is possible). - Emeric Deutsch, Dec 14 2007
Row 0 has 1 term; row n (n>=1) has floor((n+2)/3) terms. Row sums are the Catalan numbers (A000108). Column 0 yields A135337. - Emeric Deutsch, Dec 14 2007
LINKS
A. Sapounakis, I. Tasoulas and P. Tsikouras, Counting strings in Dyck paths, Discrete Math., 307 (2007), 2909-2924.
FORMULA
G.f.: G(t,z)=1+zC^2/[1+(1-t)z^3*C^4], where C=[1-sqrt(1-4z)]/(2z) is the g.f. of the Catalan numbers (A000108). - Emeric Deutsch, Dec 14 2007
EXAMPLE
Triangle begins:
1
1
2
5
13 1
36 6
105 27
320 108 1
1011 409 10
3289 1508 65
10957 5491 347 1
...
T(5,1)=6 because we have U(DUUU)UDDDD, U(DUUU)DUDDD, U(DUUU)DDUDD, U(DUUU)DDDUD, UDU(DUUU)DDD and UUD(DUUU)DDD (the DUUU's starting at level 1 are shown between parentheses).
MAPLE
G:=1+z*C^2/(1+(1-t)*z^3*C^4): C:=((1-sqrt(1-4*z))*1/2)/z: Gser:=simplify(series(G, z=0, 16)): for n from 0 to 14 do P[n]:=sort(coeff(Gser, z, n)) end do: 1; for n from 0 to 14 do seq(coeff(P[n], t, j), j=0..floor((n-1)*1/3)) end do; # yields sequence in triangular form; Emeric Deutsch, Dec 14 2007
CROSSREFS
Sequence in context: A135305 A114463 A135309 * A135329 A114508 A243366
KEYWORD
nonn,tabf
AUTHOR
N. J. A. Sloane, Dec 07 2007
EXTENSIONS
More terms from Emeric Deutsch, Dec 14 2007
STATUS
approved