A057175 Numbers k such that (9^k + 1)/10 is a prime.

3, 59, 223, 547, 773, 1009, 1823, 3803, 49223, 193247, 703393, 860029, 2698541

Offset

1,1

Comments

Repunit primes in base -9. - Paul Bourdelais

Links

Table of n, a(n) for n=1..13.

Paul Bourdelais, A Generalized Repunit Conjecture

H. Dubner and T. Granlund, Primes of the Form (b^n+1)/(b+1), J. Integer Sequences, 3 (2000), #P00.2.7.

Henri Lifchitz, Mersenne and Fermat primes field

Eric Weisstein's World of Mathematics, Repunit

Mathematica

lst={}; Do[p=(9^n+1)/10; If[PrimeQ[p], AppendTo[lst, n]], {n, 7!}]; lst (* Vladimir Joseph Stephan Orlovsky, Sep 29 2008 *)
Select[Range[4000], PrimeQ[(9^# + 1)/10] &] (* Vincenzo Librandi, Aug 03 2015 *)

Prog

(PFGW) pfgw -b2 -f10 bNeg9.txt::
ABC2 (9^$a+1)/10 // -f{4*$a}
a: primes from 3 to 1e6}
(Magma) [n: n in [0..800] | IsPrime((9^n + 1) div 10 )]; // Vincenzo Librandi, Aug 03 2015
(PARI) first(m)=my(v=vector(m)); t=0; for(i=1, m, while(!isprime((9^t + 1)\10), t++); v[i]=t; t++; ); v; \\ Anders Hellström, Aug 16 2015

Crossrefs

Sequence in context: A002148 A290977 A200957 * A142642 A395339 A201850

Adjacent sequences: A057172 A057173 A057174 * A057176 A057177 A057178

Keyword

nonn,more

Author

N. J. A. Sloane, Sep 15 2000

Extensions

a(9) from Paul Bourdelais, Oct 22 2007

a(10) from Paul Bourdelais, Feb 01 2010

a(11) from Paul Bourdelais, Aug 03 2015

a(12) from Paul Bourdelais, Sep 23 2020

a(13) from Paul Bourdelais, Feb 02 2026

Status

approved