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A103092
Numbers n such that 9*10^n-7 is prime.
1
0, 1, 6, 9, 10, 12, 13, 23, 61, 194, 233, 549, 765, 973, 1061, 1186, 1853, 3713, 6789, 7254, 7765, 9025, 10855, 23640, 31440, 31839, 32287, 120342, 132148
OFFSET
1,3
COMMENTS
Also numbers n such that 8*10^n + 9*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
a(30) > 3*10^5. Robert Price, Oct 19 2023
FORMULA
a(n) = A101079(n-1) + 1 for n>1.
EXAMPLE
For n=0, 9*10^n-7=2 which is prime, so 0 is in the sequence.
MATHEMATICA
Do[ If[ PrimeQ[9*10^n - 7], Print[n]], {n, 0, 10000}]
PROG
(Magma) [n: n in [0..300] | IsPrime(9*10^n-7)]; // Vincenzo Librandi, Sep 05 2015
(PARI) is(n)=ispseudoprime(9*10^n-7) \\ Charles R Greathouse IV, Jun 12 2017
CROSSREFS
Sequence in context: A066385 A226913 A293826 * A337940 A104523 A091886
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 19 2005
EXTENSIONS
One more term from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(23)-a(26) from Kamada data by Robert Price, Dec 14 2010
Inserted a(1)=0 by Robert Price, Sep 04 2015
a(28)-a(29) from Robert Price, Sep 04 2015
STATUS
approved