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Search: id:A132153
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| A132153 |
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Largest prime <= square root of 10^n. |
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+0
2
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| 3, 7, 31, 97, 313, 997, 3137, 9973, 31607, 99991, 316223, 999983, 3162277, 9999991, 31622743, 99999989, 316227731, 999999937, 3162277633, 9999999967, 31622776589, 99999999977, 316227766003, 999999999989, 3162277660153, 9999999999971, 31622776601657
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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To check if an n+1 digit number is prime, u(n) is the largest prime which one needs to check is not a factor of the n+1 th digit number. For example to check a general four digit number is not prime, we need to test its divisibility by all the primes up to and including 97.
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FORMULA
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a(n)=A000040(A122121(n+1)). a(2n-1)=A003618(n). - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 06 2007
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CROSSREFS
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Adjacent sequences: A132150 A132151 A132152 this_sequence A132154 A132155 A132156
Sequence in context: A088193 A091383 A072881 this_sequence A002357 A105765 A061095
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KEYWORD
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nonn,easy
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AUTHOR
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Anthony C Robin (anthony_robin(AT)hotmail.com), Nov 01 2007
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EXTENSIONS
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More terms from njas, Jan 05 2008
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