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A153431
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a(n) is the smallest number m such that all n+1 numbers m*10^k+1 k=0,1, ...,n are prime.
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2
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1, 1, 1, 4, 28, 28, 170926, 170926, 931371868, 15538734736, 89468493268
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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COMMENTS
| If n<m and r=10^n*a(m)*a(n)-1 is prime then r has at least n+1
representations of the form p*q-(p+q)where p & q are prime.
For n>3, 7 divides a(n). a(10) is greater than 4*10^10.
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LINKS
| Prime Puzzles Two Bergot questions
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EXAMPLE
| 28+1, 280+1, 2800+1, 28000+1, 280000+1 & 2800000+1 are prime and 28 is
the smallest such number so a(5)=28.
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CROSSREFS
| Cf. A153432.
Sequence in context: A132640 A174212 A038706 * A043074 A137314 A032405
Adjacent sequences: A153428 A153429 A153430 * A153432 A153433 A153434
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KEYWORD
| more,nonn
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AUTHOR
| Farideh Firoozbakht (mymontain(AT)yahoo.com), Mar 15 2009, Mar 27 2009
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