A096209 Primes of the form 10 followed by 9's only.

109, 10999999999, 1099999999999, 1099999999999999999, 109999999999999999999999, 1099999999999999999999999999999, 10999999999999999999999999999999999999, 109999999999999999999999999999999999999, 109999999999999999999999999999999999999999999999999999

Offset

1,1

Comments

Or, primes of the form 10^k + 10^(k-1) - 1.

Number of 9's in a(n) is given by A111391(n). - Daniel Starodubtsev, Jan 06 2020

Links

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

Formula

a(n) = 11*10^A111391(n) - 1 = A198700(A111391(n)). - Elmo R. Oliveira, Jun 14 2025

Mathematica

t = {}; Do[m = n; p = 10^(n + 1) + (10^n - 1); If[PrimeQ[p], AppendTo[t, p]], {n, 165}]; t (* Robert G. Wilson v, Feb 24 2006 *)

Prog

(PARI) f(n) = for(x=1, n, y=10^x+10^(x-1)-1; if(ispseudoprime(y), print1(y", ")))

Crossrefs

Cf. A111391, A113628, A113629, A113630.

Primes in A198700.

Sequence in context: A190827 A125044 A352466 * A287469 A266217 A229084

Adjacent sequences: A096206 A096207 A096208 * A096210 A096211 A096212

Keyword

base,nonn

Author

Cino Hilliard, Jul 28 2004

Extensions

Entry revised by N. J. A. Sloane, Apr 01 2006

a(8)-a(9) from Michel Marcus, Dec 27 2025

Status

approved