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A090519 Smallest prime p such that floor((10^n)/p) is prime, or 0 if no such number exists. 3
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; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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.

LINKS

Table of n, a(n) for n=1..50.

EXAMPLE

a(5) = 89, as floor((10^5)/89) = 1123 is the largest such prime.

MATHEMATICA

<<NumberTheory`; Do[k = 2; While[ !PrimeQ[Floor[10^n / k]], k = NextPrime[k]]; Print[k], {n, 1, 50}] (* Ryan Propper, Jun 19 2005 *)

CROSSREFS

Cf. A090517, A090518, A090520.

Sequence in context: A061385 A304815 A156179 * A018540 A045388 A118796

Adjacent sequences:  A090516 A090517 A090518 * A090520 A090521 A090522

KEYWORD

base,nonn

AUTHOR

Amarnath Murthy, Dec 07 2003

EXTENSIONS

Corrected and extended by Ryan Propper, Jun 19 2005

STATUS

approved

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Last modified June 21 12:03 EDT 2021. Contains 345363 sequences. (Running on oeis4.)