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A056797
Numbers k such that 9*10^k+1 is prime.
11
3, 4, 5, 9, 22, 27, 36, 57, 62, 78, 201, 537, 696, 790, 905, 1038, 66886, 70500, 91836, 100613, 127240, 380734, 583696, 719055, 823037, 862868
OFFSET
1,1
COMMENTS
a(22) > 2*10^5. - Robert Price, Jan 21 2015
FORMULA
a(n) = A100997(n) + 1.
EXAMPLE
For k=9 we have (9*(10^9))+1 = 9000000001, which is prime.
MATHEMATICA
Do[ If[ PrimeQ[9*10^n + 1], Print[n]], {n, 0, 10000}]
PROG
(Magma) [n: n in [0..1000] | IsPrime(9*10^n+1)]; // Vincenzo Librandi, May 25 2015
(PARI) is(n)=ispseudoprime(9*10^n+1) \\ Charles R Greathouse IV, Feb 17 2017
CROSSREFS
Cf. A056806 (4*10^k+1 is prime), A100997.
Sequence in context: A063781 A257041 A346603 * A029727 A086186 A365578
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Aug 22 2005
EXTENSIONS
a(18)-a(19) from Kamada data by Robert Price, Dec 14 2010
a(20) from Predrag Kurtovic, Sep 23 2013
a(21) from Robert Price, Jan 21 2015
a(22)-a(23) from Kamada data by Mohammed Yaseen, Jul 20 2021
a(24) from Predrag Kurtovic, Apr 18 2024
a(25)-a(26) from Predrag Kurtovic, Apr 22 2024
STATUS
approved