Near-repdigit

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This site will be down for maintenance beginning noon CDT (5pm UTC) Wed April 14The Prime Pages keeps a list of the 5000 largest known primes, plus a few each of certain selected archivable forms and classes. These forms are defined in this collection's home page. This page is about one of those forms. Comments and suggestions requested.

Definitions and Notes

A repunit is a number of the form 11111...111 (repeated units). In base two (binary), these are the Mersenne primes. In base ten, just a few are known. If we repeat any other digit, then we get a composite (e.g., 777777 is divisible by 7).

To get a more general form, two things have been tried:

Let one of the digits differ from one--these are the near repunit primes.
Let all but one of the digits be the same, these are the near repdigit primes (and include the near repunit primes).

Record Primes of this Type

>rank prime digits who when comment

1 993 · 10^1768283 - 1 1768286 L4879 Feb 2019 Near - repdigit
2 9 · 10^1762063 - 1 1762064 L4879 Aug 2020 Near - repdigit
3 8 · 10^1715905 - 1 1715906 L4879 Aug 2020 Near - repdigit
4 9992 · 10^1567410 - 1 1567414 L4879 Aug 2020 Near - repdigit
5 99 · 10^1536527 - 1 1536529 L4879 Feb 2019 Near - repdigit
6 992 · 10^1533933 - 1 1533936 L4879 Feb 2019 Near - repdigit
7 92 · 10^1439761 - 1 1439763 L4789 Dec 2020 Near - repdigit
8 2 · 10^1059002 - 1 1059003 L3432 Sep 2013 Near - repdigit
9 93 · 10^1029523 - 1 1029525 L4789 Jan 2019 Near - repdigit
10 9 · 10^1009567 - 1 1009568 L3735 Sep 2016 Near - repdigit
11 96 · 10⁸⁴⁶⁵¹⁹ - 1 846521 L2425 Sep 2011 Near - repdigit
12 92 · 10⁸³³⁸⁵² - 1 833854 L4789 Apr 2018 Near - repdigit
13 93 · 10⁶⁴²²²⁵ - 1 642227 L4789 Mar 2020 Near - repdigit
14 8 · 10⁶⁰⁸⁹⁸⁹ - 1 608990 p297 May 2011 Near - repdigit
15 92 · 10⁵⁴⁴⁹⁰⁵ - 1 544907 L3735 May 2015 Near - repdigit
16 5 · 10⁵¹¹⁰⁵⁶ - 1 511057 p297 Mar 2011 Near - repdigit
17 95 · 10⁴⁶⁶⁰⁰² - 1 466004 L3735 May 2014 Near - repdigit
18 5 · 10⁴⁶⁴⁸⁴³ - 1 464844 p297 Feb 2011 Near - repdigit
19 5 · 10⁴⁴⁵⁷⁷³ - 1 445774 p297 Jan 2011 Near - repdigit
20 999999998 · 10⁴¹⁹³⁴³ - 1 419352 L1958 Apr 2019 Near - repdigit

References

Caldwell89
C. Caldwell, "The near repdigit primes 333 ^... 331," J. Recreational Math., 21:4 (1989) 299--304.
Caldwell90
C. Caldwell, "The near repdigit primes A_nB, AB_n, and UBASIC," J. Recreational Math., 22:2 (1990) 100--109.
CD95
C. Caldwell and H. Dubner, "The near repunit primes 1_n-k-10₁1_k," J. Recreational Math., 27 (1995) 35--41.
CD97
C. Caldwell and H. Dubner, "The near repdigit primes A_n-k-1B₁A_k, especially 9_n-k-18₁9_k," J. Recreational Math., 28:1 (1996-97) 1--9.
Heleen98
Heleen, J. P., "More near-repunit primes 1_n-k-1D₁1_k, D=2,3, ..., 9," J. Recreational Math., 29:3 (1998) 190--195.
Williams78b
H. C. Williams, "Some primes with interesting digit patterns," Math. Comp., 32 (1978) 1306--1310. Corrigendum in 39 (1982), 759. MR 58:484