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A056805 Numbers n such that 6*10^n+1 is prime. 10
0, 1, 2, 8, 9, 15, 20, 26, 38, 45, 65, 112, 244, 303, 393, 560, 839, 1009, 1019, 1173, 1334, 2236, 2629, 4426, 8848, 20812, 37744, 72926, 86287 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

From the Kamada data, Edward Trice reports that 231617 and 522127 are in this sequence. But these may not be the next ones.  There are no others less than 2*10^5, however. - Robert Price, Jul 09 2015

LINKS

Table of n, a(n) for n=1..29.

Makoto Kamada, Prime numbers of the form 600...001.

Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.

FORMULA

a(n) = A101517(n-1) + 1.

EXAMPLE

n=2 => (6*10^2+1)=601, which is prime.

MATHEMATICA

Do[ If[ PrimeQ[ 6*10^n + 1], Print[ n ]], {n, 0, 10000}]

PROG

(PARI) is(n)=isprime(6*10^n+1) \\ Charles R Greathouse IV, Feb 17 2017

CROSSREFS

Cf. A056716, A101517.

Sequence in context: A032928 A287564 A158458 * A226825 A046679 A004999

Adjacent sequences:  A056802 A056803 A056804 * A056806 A056807 A056808

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Aug 22 2000

EXTENSIONS

a(22)-a(25) from Hugo Pfoertner, Feb 11 2004

a(26)=20812 from Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 27 2007

a(27)=37744 from Jason Earls, Mar 07 2008

a(28)-a(29) from Kamada data by Robert Price, Dec 09 2010

STATUS

approved

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Last modified December 5 17:42 EST 2019. Contains 329768 sequences. (Running on oeis4.)