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A118928 a(n) = Sum_{k=0..[n/2]} C(n-k,k)*C(n-k,k+1)/(n-k) * a(k), with a(0)=1. 0
1, 1, 1, 2, 4, 8, 17, 38, 92, 238, 643, 1790, 5076, 14573, 42241, 123484, 364052, 1082602, 3247759, 9829820, 30019326, 92517644, 287805801, 903822922, 2865339252, 9168572009, 29601077285, 96377791839, 316264456921 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

Invariant column vector V under matrix product A089732 *V = V: a(n) = Sum_{k=0,[n/2]} A089732 (n,k)*a(k), where A089732(n,k) = number of peakless Motzkin paths of length n having k (1,1) steps.

LINKS

Table of n, a(n) for n=0..28.

PROG

(PARI) {a(n)=if(n==0, 1, sum(k=0, n\2, binomial(n-k, k)*binomial(n-k, k+1)/(n-k)*a(k)))}

CROSSREFS

Cf. A089732.

Sequence in context: A081124 A090901 A101516 * A325921 A049312 A132043

Adjacent sequences:  A118925 A118926 A118927 * A118929 A118930 A118931

KEYWORD

nonn

AUTHOR

Paul D. Hanna, May 06 2006

STATUS

approved

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Last modified August 7 15:20 EDT 2020. Contains 336276 sequences. (Running on oeis4.)