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Search: id:A118928
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| A118928 |
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a(n) = Sum_{k=0..[n/2]} C(n-k,k)*C(n-k,k+1)/(n-k) * a(k), with a(0)=1. |
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+0
1
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| 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
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OFFSET
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0,4
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COMMENT
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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.
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PROGRAM
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(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)))}
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CROSSREFS
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Cf. A089732.
Sequence in context: A081124 A090901 A101516 this_sequence A049312 A132043 A055545
Adjacent sequences: A118925 A118926 A118927 this_sequence A118929 A118930 A118931
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KEYWORD
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nonn
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AUTHOR
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Paul D. Hanna (pauldhanna(AT)juno.com), May 06 2006
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