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Search: id:A090519
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| A090519 |
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Smallest prime p such that floor[(10^n)/p] is prime, or 0 if no such number exists. |
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+0
4
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| 2, 13, 23, 13, 89, 19, 7, 47, 67, 13, 17, 157, 17, 313, 107, 409, 151, 773, 149, 409, 109, 13, 29, 211, 7, 19, 149, 431, 859, 43, 109, 167, 277, 13, 2293, 173, 907, 107, 1087, 617, 449, 1013, 73, 1249, 743, 109, 233, 499, 191, 479
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Conjecture: No term is zero. Subsidiary Sequence: Number of primes in floor[(10^n)/p], p is a prime. a(1) = 3, the primes are 10/2, floor[10/3], and 10/5.
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EXAMPLE
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a(5) = 89, as floor[(10^5)/89]= 1123 is the largest such prime.
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MATHEMATICA
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<<NumberTheory`; Do[k = 2; While[ !PrimeQ[Floor[10^n / k]], k = NextPrime[k]]; Print[k], {n, 1, 50}] (Propper)
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CROSSREFS
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Cf. A090517, A090518, A090520.
Sequence in context: A085509 A127485 A061385 this_sequence A018540 A045388 A045389
Adjacent sequences: A090516 A090517 A090518 this_sequence A090520 A090521 A090522
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KEYWORD
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base,nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Dec 07 2003
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EXTENSIONS
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Corrected and extended by Ryan Propper (rpropper(AT)stanford.edu), Jun 19 2005
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