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Search: id:A156234
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| 1, 1, 5, 10, 30, 63, 170, 355, 880, 1875, 4349, 9189, 20810, 43355, 95140, 198247, 424527, 875965, 1849535, 3781820, 7873167, 16005196, 32883560, 66390850, 135198990, 271051271, 546931398, 1090751095, 2183512495, 4329540830
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OFFSET
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0,3
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COMMENT
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Compare to g.f. of partition numbers: exp( Sum_{n>=1} sigma(n)*x^n/n ),
and to the g.f. of Fibonacci numbers: exp( Sum_{n>=1} A000204(n)*x^n/n ) where A000204 is the Lucas numbers.
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FORMULA
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a(n) = (1/n)*Sum_{k=1..n} sigma(n)*A000204(k)*a(n-k) for n>0, with a(0) = 1.
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EXAMPLE
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G.f.: A(x) = 1 + x + 5*x^2 + 10*x^3 + 30*x^4 + 63*x^5 + 170*x^6 + 355*x^7 +...
log(A(x)) = x + 3*3*x^2/2 + 4*4*x^3/3 + 7*7*x^4/4 + 6*11*x^5/5 + 12*18*x^6/6 +...
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PROGRAM
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(PARI) {a(n)=polcoeff(exp(sum(k=1, n, sigma(k)*(fibonacci(k-1)+fibonacci(k+1))*x^k/k)+x*O(x^n)), n)}
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CROSSREFS
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Cf. A000203 (sigma), A000204 (Lucas), A000041 (partitions), A000045 (Fibonacci).
Sequence in context: A053818 A133629 A156302 this_sequence A048010 A002571 A077916
Adjacent sequences: A156231 A156232 A156233 this_sequence A156235 A156236 A156237
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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), Feb 06 2009
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