A090517 -id:A090517 - cp's OEIS frontend

A090518 Primes arising in A090517, or 0 if A090517(n) = 0.

5, 11, 83, 769, 3571, 52631, 1428571, 3703703, 83333333, 769230769, 5882352941, 13513513513, 588235294117, 7142857142857, 12195121951219, 151515151515151, 2777777777777777, 22727272727272727, 1111111111111111111

Offset: 1

Amarnath Murthy, Dec 07 2003

Conjecture: No term is zero.

Cf. A090517, A090519, A090520.

A090518(n)={ local(k,tenn) ; k=1 ; tenn=10^n ; while(1, if( isprime(floor(tenn/k)), return(floor(tenn/k)) ) ; k++ ; ) ; } { for(n=1,40, print1(A090518(n),",") ; ) } - R. J. Mathar, Nov 19 2006

Corrected and extended by R. J. Mathar, Nov 19 2006

A090519 Smallest prime p such that floor((10^n)/p) is prime, or 0 if no such number exists.

Original entry on oeis.org

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

Offset: 1

Amarnath Murthy, Dec 07 2003

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.

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

Robert Israel, Table of n, a(n) for n = 1..1800

Cf. A090517, A090518, A090520.

f:= proc(n) local t,p;
t:= 10^n;
p:= 1;
while p < t/2 do
  p:= nextprime(p);
  if isprime(floor(t/p)) then return p fi
od;
0
end proc:
map(f, [$1..50]); # Robert Israel, Jul 30 2023

Mathematica
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<Ryan Propper, Jun 19 2005 *)
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Corrected and extended by Ryan Propper, Jun 19 2005

A090520 Primes arising in A090519, or 0 if A090519(n)= 0.

Original entry on oeis.org

5, 7, 43, 769, 1123, 52631, 1428571, 2127659, 14925373, 769230769, 5882352941, 6369426751, 588235294117, 319488817891, 9345794392523, 24449877750611, 662251655629139, 1293661060802069, 67114093959731543, 244498777506112469

Offset: 1

Amarnath Murthy, Dec 07 2003

Conjecture: No term is zero.

Cf. A090517, A090518, A090519.

A090520(n)={ local(p,tenn) ; p=2 ; tenn=10^n ; while(tenn/p>=2, if( isprime(floor(tenn/p)), return(floor(tenn/p)) ) ; p=nextprime(p+1) ; ) ; return(0) ; } { for(n=1,40, print1(A090520(n),",") ; ) } - R. J. Mathar, Nov 19 2006

Corrected and extended by R. J. Mathar, Nov 19 2006

cp's OEIS Frontend

A090518 Primes arising in A090517, or 0 if A090517(n) = 0.

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A090519 Smallest prime p such that floor((10^n)/p) is prime, or 0 if no such number exists.

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A090520 Primes arising in A090519, or 0 if A090519(n)= 0.

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