

A097611


Triangle read by rows: T(n,k) is number of Motzkin paths of length n having k peaks at height 1.


0



1, 1, 1, 1, 2, 2, 5, 3, 1, 12, 6, 3, 29, 15, 6, 1, 72, 38, 13, 4, 183, 96, 33, 10, 1, 473, 246, 87, 24, 5, 1239, 641, 229, 63, 15, 1, 3282, 1692, 606, 172, 40, 6, 8777, 4512, 1620, 470, 110, 21, 1, 23665, 12136, 4370, 1284, 311, 62, 7, 64261, 32887, 11874, 3523, 880, 180
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OFFSET

0,5


COMMENTS

Row sums are the Motzkin numbers (A001006). Column 0 is A089372.


LINKS

Table of n, a(n) for n=0..61.


FORMULA

G.f.= 2/[1z+2z^22tz^2+sqrt(12z3z^2)].


EXAMPLE

Triangle begins:
1;
1;
1,1;
2,2;
5,3,1;
12,6,3;
Row n has 1+floor(n/2) terms.
T(5,2)=3 because H(UD)(UD), (UD)H(UD), (UD)(UD)H are the only Motzkin paths of length 5 with 2 peaks at height 1 (shown between parentheses); here U=(1,1),
H=(1,0) and D=(1,1).


MAPLE

G := 2/(1z+sqrt(12*z3*z^2)+2*z^22*z^2*t): Gser:=simplify(series(G, z=0, 16)): P[0]:=1: for n from 1 to 15 do P[n]:=sort(coeff(Gser, z^n)) od: seq(seq(coeff(t*P[n], t^k), k=1..1+floor(n/2)), n=0..15);


CROSSREFS

Cf. A001006, A089372.
Sequence in context: A038041 A197591 A097891 * A135376 A132850 A076561
Adjacent sequences: A097608 A097609 A097610 * A097612 A097613 A097614


KEYWORD

nonn,tabf


AUTHOR

Emeric Deutsch, Aug 30 2004


STATUS

approved



