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.

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A055559 Primes of the form 2999...999.

Original entry on oeis.org

2, 29, 2999, 2999999, 29999999, 29999999999999999999, 2999999999999999999999999999, 29999999999999999999999999999999999999999999, 29999999999999999999999999999999999999999999999999999999
Offset: 1

Views

Author

Labos Elemer, Jul 10 2000

Keywords

Comments

a(9)=29999999999999999999999999999999999999999999999999999999. - Vincenzo Librandi, Aug 07 2010
The next term (a(10)) has 208 digits, and a(11) has 1312 digits. - Harvey P. Dale, Jan 22 2023

Examples

			3*10^k - 1 is prime for k = 0, 1, 3, 6, 7, 19, ... (A056703). k gives the number of 9's in these numbers.

Crossrefs

Cf. A051200, A056703, A056703.

Programs

  • Mathematica
    Select[Table[FromDigits[PadRight[{2}, n, 9]], {n, 60}], PrimeQ] (* Harvey P. Dale, Jan 22 2023 *)

Formula

a(n) = A198698(A056703(n)) = 3*10^A056703(n) - 1. - Amiram Eldar, Mar 16 2025

Extensions

Erroneous Formula entry removed by Jon E. Schoenfield, Jan 14 2018
Extended by Harvey P. Dale, Jan 22 2023
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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