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URL: https://oeis.org/A057175

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A057175
Numbers k such that (9^k + 1)/10 is a prime.
21
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
H. Dubner and T. Granlund, Primes of the Form (b^n+1)/(b+1), J. Integer Sequences, 3 (2000), #P00.2.7.
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 A201850 A013526
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