cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-4 of 4 results.

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

Views

Author

Amarnath Murthy, Dec 07 2003

Keywords

Comments

Conjecture: No term is zero.

Crossrefs

Cf. A090517, A090518, A090519.

Programs

  • PARI
    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

Extensions

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

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

Original entry on oeis.org

5, 11, 83, 769, 3571, 52631, 1428571, 3703703, 83333333, 769230769, 5882352941, 13513513513, 588235294117, 7142857142857, 12195121951219, 151515151515151, 2777777777777777, 22727272727272727, 1111111111111111111
Offset: 1

Views

Author

Amarnath Murthy, Dec 07 2003

Keywords

Comments

Conjecture: No term is zero.

Crossrefs

Cf. A090517, A090519, A090520.

Programs

  • PARI
    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

Extensions

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

A090517 Least k such that floor[(10^n)/k] is prime.

Original entry on oeis.org

2, 9, 12, 13, 28, 19, 7, 27, 12, 13, 17, 74, 17, 14, 82, 66, 36, 44, 9, 36, 21, 13, 9, 90, 7, 19, 149, 51, 321, 35, 12, 14, 140, 13, 28, 42, 34, 36, 153, 155, 133, 46, 73, 106, 162, 109, 122, 42, 62, 422, 29, 231, 38, 34, 340, 295, 151, 197, 94, 19, 17, 83, 131, 66, 36
Offset: 1

Views

Author

Amarnath Murthy, Dec 07 2003

Keywords

Examples

			a(1) = 2 as 10/2 = 5 is a prime. a(3) = 12 as floor[1000/12] = 83 is prime.

Crossrefs

Cf. A090518, A090519, A090520.

Programs

  • Mathematica
    lkp[n_]:=Module[{k=2,c=10^n},While[!PrimeQ[Floor[c/k]],k++];k]; Array[ lkp,70] (* Harvey P. Dale, Jul 09 2018 *)

Extensions

Corrected and extended by Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Jan 28 2004
Further terms from David Wasserman, Dec 20 2005

A364644 Numbers k such that floor(10^k/7) is prime.

Original entry on oeis.org

7, 25, 355, 823
Offset: 1

Views

Author

Robert Israel, Jul 31 2023

Keywords

Comments

Numbers k such that A090519(k) = 7.
All terms == 1 (mod 6).
Numbers k such that (10^k-3)/7 is prime.
a(5) > 20000 if it exists. - Hugo Pfoertner, Jul 31 2023

Examples

			a(1) = 7 is a term because floor(10^7/7) = 1428571 is prime.

Crossrefs

Cf. A090519.

Programs

  • Maple
    select(n -> isprime(floor(10^n/7)),[seq(i,i=1..1000,6)]);
Showing 1-4 of 4 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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