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Search: id:A115658
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| A115658 |
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a(n) is the smallest square-free a(n-1)-almost prime; a(1) = 1. |
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+0
2
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OFFSET
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1,2
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COMMENT
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A subsequence of A002110. a(5) = prime(a(4))# = prime(30030)# = 350741# [= A002110(30030)], a 152104-digit number. Compare with A007097 (primeth recurrence): The current sequence is analogously the primorial(e)th recurrence but grows faster even than A014221 (Ackermann function A_3(n+1)). This suggests considering the analogues also for factorials, hyperfactorials, etc., to see which may fit as OEIS entries.
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FORMULA
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a(n) = prime(a(n-1))# = prod(k=1, a(n-1), prime(k)) = A002110(a(n-1)) for n >= 2; a(1) = 1.
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EXAMPLE
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a(4) = prime(a(3))# = prime(6)# = 13# = 2*3*5*7*11*13 = 30030 [= A002110(6)].
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CROSSREFS
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Cf. A014221 (similar but not square-free), A002110 (primorials), A007097.
Sequence in context: A162146 A055698 A121167 this_sequence A005607 A161563 A135408
Adjacent sequences: A115655 A115656 A115657 this_sequence A115659 A115660 A115661
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KEYWORD
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easy,nonn
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AUTHOR
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Rick L. Shepherd (rshepherd2(AT)hotmail.com), Jan 28 2006
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