

A056797


Numbers n such that 9*10^n+1 is prime.


7



3, 4, 5, 9, 22, 27, 36, 57, 62, 78, 201, 537, 696, 790, 905, 1038, 66886, 70500, 91836, 100613, 127240
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OFFSET

1,1


COMMENTS

a(22) > 2*10^5.  Robert Price, Jan 21 2015


LINKS

Table of n, a(n) for n=1..21.
Makoto Kamada, Prime numbers of the form 900...001.
Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.
Index entries for primes involving repunits.


FORMULA

a(n) = A100997(n) + 1.


EXAMPLE

For n=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


CROSSREFS

Cf. A056806 (4*10^n+1 is prime), A100997.
Sequence in context: A080552 A215176 A257041 * A029727 A086186 A014463
Adjacent sequences: A056794 A056795 A056796 * A056798 A056799 A056800


KEYWORD

more,nonn,changed


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


STATUS

approved



