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A046461
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Numbers n such that concatenation of numbers from 1 to n is a semiprime.
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3
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OFFSET
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1,1
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COMMENTS
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Contribution from Sean A. Irvine, Apr 15 2010: (Start)
5053 and 9706 are definite members of the sequence.
The next potential member is 1051 (a factor is needed to establish membership) (End)
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LINKS
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Table of n, a(n) for n=1..5.
P. De Geest, Normal Smarandache Concatenated Numbers, Prime factors from 1 up to n
C. Rivera, Primes by Listing
M. Fleuren, Factors and primes of Smarandache sequences.
M. Fleuren, Smarandache Factors and Reverse factors
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EXAMPLE
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Sm(691)=1304238680165623831238651513722972177904593843651*C1916, so Sm(691) is not a semiprime and 691 is not a member of this sequence.
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CROSSREFS
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Cf. A046460.
Sequence in context: A007677 A042773 A042173 * A084590 A041135 A041379
Adjacent sequences: A046458 A046459 A046460 * A046462 A046463 A046464
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KEYWORD
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nonn,hard,base,more
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AUTHOR
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Patrick De Geest, Aug 15 1998.
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EXTENSIONS
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Simplified definition by Sean A. Irvine, Mar 29 2010
a(5) from Sean A. Irvine, Mar 29 2010
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STATUS
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approved
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