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A137966
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G.f. satisfies A(x) = 1+x + x^2*A(x)^6.
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4
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1, 1, 1, 6, 21, 86, 396, 1812, 8607, 41958, 207333, 1040234, 5281965, 27078756, 140021248, 729369474, 3823598232, 20158251814, 106809280563, 568471343322, 3037782047947, 16292380484454, 87669285293451, 473172657154822
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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FORMULA
| a(n) = Sum_{k=0..n-1} C(n-k,k)/(n-k) * C(6*k,n-k-1) for n>0 with a(0)=1. [From Paul D. Hanna (pauldhanna(AT)juno.com), Jun 16 2009]
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PROG
| (PARI) {a(n)=local(A=1+x*O(x^n)); for(i=0, n, A=1+x*(1+x*A^6)^1); polcoeff(A, n)}
(PARI) a(n)=if(n==0, 1, sum(k=0, n-1, binomial(n-k, k)/(n-k)*binomial(6*k, n-k-1))) [From Paul D. Hanna (pauldhanna(AT)juno.com), Jun 16 2009]
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CROSSREFS
| Cf. A137967, A137965; A019497, A137954, A137959.
Sequence in context: A199115 A191597 A088556 * A005498 A002222 A006359
Adjacent sequences: A137963 A137964 A137965 * A137967 A137968 A137969
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KEYWORD
| nonn
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AUTHOR
| Paul D. Hanna (pauldhanna(AT)juno.com), Feb 26 2008
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