Voozh

A055559

Primes of the form 2999...999.

2, 29, 2999, 2999999, 29999999, 29999999999999999999, 2999999999999999999999999999, 29999999999999999999999999999999999999999999, 29999999999999999999999999999999999999999999999999999999

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

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

LINKS

Table of n, a(n) for n=1..9.

FORMULA

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

EXAMPLE

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.

MATHEMATICA

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

CROSSREFS

Cf. A051200, A056703, A056703.

Sequence in context: A112784 A252042 A295426 * A350858 A345041 A114533

Adjacent sequences: A055556 A055557 A055558 * A055560 A055561 A055562

KEYWORD

base,nonn

AUTHOR

Labos Elemer, Jul 10 2000

EXTENSIONS

Erroneous Formula entry removed by Jon E. Schoenfield, Jan 14 2018

Extended by Harvey P. Dale, Jan 22 2023

STATUS

approved

URL: https://oeis.org/A055559

⇱ A055559 - OEIS