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A057175
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Numbers n such that (9^n + 1)/10 is a prime.
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21
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3, 59, 223, 547, 773, 1009, 1823, 3803, 49223, 193247, 703393, 860029
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OFFSET
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1,1
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COMMENTS
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LINKS
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Eric Weisstein's World of Mathematics, Repunit
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MATHEMATICA
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PROG
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(PFGW v3.3.1 from primeform.net) 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
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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a(9) corresponds to a probable prime, was discovered on Oct 22 2007. Trial factored to 1E11 with Fermat base 2 primality test. - Paul Bourdelais
a(10) corresponds to a probable prime, discovered by Paul Bourdelais, Feb 01 2010
a(11) corresponds to a probable prime, discovered by Paul Bourdelais, Aug 03 2015
a(12) corresponds to a probable prime, discovered by Paul Bourdelais, Sep 23 2020
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STATUS
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approved
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