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A103815
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a(n) = -1 + Product_{k=1..n} Fibonacci(k).
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2
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0, 0, 1, 5, 29, 239, 3119, 65519, 2227679, 122522399, 10904493599, 1570247078399, 365867569267199, 137932073613734399, 84138564904377983999, 83044763560621070207999, 132622487406311849122175999, 342696507457909818131702783999, 1432814097681520949608649339903999
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OFFSET
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1,4
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COMMENTS
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a(n) asymptotic to Phi^A000217(n). Prime for n = 4, 5, 6, 7, 8, 14, 15. Semiprime for n = 9, 10, 11, 20.
Thus, it is not until the 12th element in the sequence that we get number with more than 2 prime factors: 1570247078399 = 37 * 59 * 16349 * 43997. - Jonathan Vos Post, Dec 08 2012
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LINKS
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FORMULA
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a(n) = Product[Fibonacci[k], {k, 1, n}]-1 = Product[A000045[k], {k, 1, n}]-1.
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EXAMPLE
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a(15) = 1 * 1 * 2 * 3 * 5 * 8 * 13 * 21 * 34 * 55 * 89 * 144 * 233 * 377 * 610 - 1 = 84138564904377983999 is prime.
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MAPLE
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F:= n-> (<<0|1>, <1|1>>^n)[1, 2]:
a:= n-> -1 + mul(F(i), i=1..n):
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MATHEMATICA
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FoldList[Times, Fibonacci[Range[20]]]-1 (* Harvey P. Dale, Aug 29 2021 *)
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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