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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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified May 26 23:22 EDT 2015. Contains 257849 sequences.