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.

Previous Showing 41-46 of 46 results.

A099663 a(n) is the largest prime before A002276(n).

Original entry on oeis.org

19, 211, 2221, 22193, 222199, 2222219, 22222199, 222222193, 2222222137, 22222222189, 222222222169, 2222222222197, 22222222222201, 222222222222151, 2222222222222203, 22222222222222153, 222222222222222221, 2222222222222222177, 22222222222222222169, 222222222222222222149, 2222222222222222222161
Offset: 2

Views

Author

Labos Elemer, Nov 17 2004

Keywords

Examples

			n=2: 19 is before 22.

Crossrefs

Cf. A007917, A002276.
Cf. A003618, A003617, A096497, A096498, A068104, A002275-A002283, A099656-A099669.

Programs

  • Mathematica
    Table[NextPrime[2(10^n-1)/9, -1], {n, 2, 35}]
Drop[NextPrime[#,-1]&/@LinearRecurrence[{11,-10},{0,2},20],2] (* Harvey P. Dale, Dec 19 2020 *)

Formula

a(n) = A007917(A002276(n)). - Michel Marcus, Jun 29 2025

Extensions

More terms from Michel Marcus, Jun 29 2025

A099665 a(n) is the largest prime before A002279(n).

Original entry on oeis.org

3, 53, 547, 5531, 55547, 555523, 5555527, 55555553, 555555541, 5555555519, 55555555543, 555555555551, 5555555555551, 55555555555541, 555555555555529, 5555555555555539, 55555555555555519, 555555555555555487, 5555555555555555533, 55555555555555555483, 555555555555555555491
Offset: 1

Views

Author

Labos Elemer, Nov 17 2004

Keywords

Examples

			n=2: 53 is before 55.

Crossrefs

Cf. A002282, A003618, A003617, A007917, A096497, A096498, A068104, A002275-A002283, A099656-A099668.

Programs

  • Mathematica
    Table[NextPrime[5*(10^n-1)/9, -1], {n, 1, 35}]
NextPrime[#,-1]&/@Table[FromDigits[PadRight[{},n,5]],{n,20}] (* Harvey P. Dale, Aug 31 2015 *)

Formula

a(n) = A007917(A002282(n)). - Amiram Eldar, Jun 29 2025

A099666 a[n] is the largest prime before A002280[n] repdigits.

Original entry on oeis.org

5, 61, 661, 6661, 66653, 666649, 6666617, 66666653, 666666653, 6666666661, 66666666643, 666666666619, 6666666666629, 66666666666647, 666666666666647, 6666666666666571, 66666666666666601, 666666666666666661
Offset: 1

Views

Author

Labos Elemer, Nov 17 2004

Keywords

Examples

			n=2: 61 is before 66.

Crossrefs

Cf. A003618, A003617, A096497, A096498, A068104, A002275-A002283, A099656-A099668.

Programs

  • Mathematica
    <

A128946 Numbers n such that the largest prime < 10^n is a twin prime member.

Original entry on oeis.org

1, 5, 14, 406, 1118, 4934
Offset: 1

Views

Author

Cino Hilliard, Apr 28 2007

Keywords

Comments

A003618(a(n)) is in A001097 (Twin primes).

Examples

			For n=1, 10^1 = 10. 7, the greatest prime < 10, is a member of the twin prime pair 5,7.

Programs

  • Mathematica
    Select[Range[410],PrimeQ[NextPrime[10^#,-1]-2]&] (* The program generates the first four terms of the sequence. *) (* Harvey P. Dale, Jul 26 2024 *)
  • PARI
    g(n)=for(x=1,n,y=precprime(10^x);if(ispseudoprime(y-2),print1(x",")))

Extensions

Edited by Ray Chandler, May 12 2007
a(5), a(6) from Donovan Johnson, Feb 21 2008

A261512 Largest n-digit lucky number.

Original entry on oeis.org

9, 99, 997, 9999, 99987, 999987, 9999997, 99999979, 999999991, 9999999997, 99999999973, 999999999937, 9999999999999, 99999999999943, 999999999999993
Offset: 1

Views

Author

Robert G. Wilson v, Aug 22 2015

Keywords

Crossrefs

Cf. A000959, A003618.

Programs

Extensions

a(11)-a(15) from Hiroaki Yamanouchi, Aug 24 2015

A330468 Numbers k where the difference (least prime > 10^k) - (greatest prime < 10^k) sets a record.

Original entry on oeis.org

1, 3, 4, 9, 16, 21, 24, 28, 34, 66, 82, 92, 117, 122, 135, 218, 232, 314, 387, 443, 478, 617, 652, 787, 1031, 1157, 1440, 1625, 1872, 1920, 2038, 2424, 2692, 3235, 3331, 3798, 4944, 5202, 5241, 5938, 7572, 7847
Offset: 1

Views

Author

Hugo Pfoertner, Mar 01 2020

Keywords

Examples

			a(1) = 1: 11 - 7 = 4;
a(2) = 3: 1009 - 997 = 12, whereas 101 - 97 = 4 <= a(1).

Crossrefs

Cf. A003617, A003618, A038804, A331834.

Programs

  • PARI
    d=0;for(k=1,500,my(t=10^k,dd=nextprime(t)-precprime(t));if(dd>d,print1(k,", ");d=dd))

Extensions

More terms from Jinyuan Wang, Mar 01 2020
a(37)-a(42) from Giovanni Resta, Mar 15 2020
Previous Showing 41-46 of 46 results.

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

Content is available under The OEIS End-User License Agreement.