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A099080
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Numbers n such that sigma(n).sigma(n-1) ... sigma(2).sigma(1) is prime (dot between numbers means concatenation).
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3
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OFFSET
| 1,1
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COMMENTS
| Numbers of digits of primes corresponding to the four known terms of this sequence are respectively 2,3,133,232.
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LINKS
| Eric Weisstein ,A Section of The World of Mathematics
C. Rivera, ,Primes by Listing, The Prime Puzzles & Problems connection.
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EXAMPLE
| 3 is in the sequence because sigma(3).sigma(2).sigma(1)=431 is prime.
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CROSSREFS
| Cf. A046035, A099077, A099078, A099079.
Sequence in context: A004854 A015169 A041953 * A132532 A108023 A041249
Adjacent sequences: A099077 A099078 A099079 * A099081 A099082 A099083
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KEYWORD
| base,more,nonn,bref
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AUTHOR
| Farideh Firoozbakht (mymontain(AT)yahoo.com), Oct 23 2004
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