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Search: id:A124499
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| A124499 |
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Number of 1-2-3-4 trees with n edges and with thinning limbs. A 1-2-3-4 tree is an ordered tree with vertices of outdegree at most 4. A rooted tree with thinning limbs is such that if a node has k children, all its children have at most k children. |
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+0
3
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| 1, 1, 2, 4, 10, 24, 62, 160, 425, 1140, 3105, 8528, 23643, 66008, 185526, 524384, 1489810, 4251852, 12184745, 35048405, 101156752, 292865417, 850314803, 2475327088, 7223400899, 21126670372, 61920289652, 181838859665
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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The sequences corresponding to k=2 (A090344), k=3 (A124497), k=4 (this A124499), k=5 (A124500), etc. approach sequence A124344, corresponding to ordered trees with thinning limbs.
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FORMULA
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In general, if M[k](z) is the g.f. of the 1-2-...-k trees with thinning limbs and C[k](z)=1+z*{C[k](z)}^k is the g.f. of the k-ary trees, then M[k](z)=M[k-1](z)*C[k](M[k-1]^(k-1)*z^k), M[1](z)=1/(1-z).
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PROGRAM
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(PARI) {a(n)=local(k=4, M=1+x*O(x^n)); for(i=1, k, M=M*sum(j=0, n, binomial(i*j, j)/((i-1)*j+1)*(x^i*M^(i-1))^j)); polcoeff(M, n)} (Paul D. Hanna)
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CROSSREFS
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Cf. A090344, A124497, A124500, A124501, A124344.
Sequence in context: A006575 A138175 A121691 this_sequence A132220 A007874 A121704
Adjacent sequences: A124496 A124497 A124498 this_sequence A124500 A124501 A124502
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KEYWORD
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nonn
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AUTHOR
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Emeric Deutsch and Louis Shapiro (deutsch(AT)duke.poly.edu, lshapiro(AT)Howard.edu), Nov 06 2006
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