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Search: id:A102589
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| A102589 |
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Numbers of the forms 4*p or q where both numbers p=(10^n-7)/3 and q=(127*10^(n-1)-7)/3 are primes. |
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2
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OFFSET
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1,1
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COMMENT
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This sequence is a subsequence of A069514 (If m is in the sequence then sigma(reversal(m)) = reversal(sigma(m))), so see Comments on A069514. There exists only four known n's such that both numbers p=(10^n-7)/3 and q=(127*10^(n-1)-7)/3 are primes, n=2,3, 4 and 6.
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EXAMPLE
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124 and 421 are in the sequence because 124=4*31 and both numbers
31=(10^2-7)/3 and 421=(127*10^(2-1)-7)/3 are primes. It seems that
there is no further term.
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CROSSREFS
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Cf. A069514, A102285.
Sequence in context: A045295 A045280 A045250 this_sequence A038645 A038859 A024017
Adjacent sequences: A102586 A102587 A102588 this_sequence A102590 A102591 A102592
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KEYWORD
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nonn
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AUTHOR
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Farideh_Firoozbakht (mymontain(AT)yahoo.com), Jan 22 2005
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