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A103065 Numbers n such that 7*10^n + 6*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
1, 2, 3, 6, 8, 18, 19, 21, 32, 48, 65, 72, 99, 120, 201, 308, 717, 968, 1344, 2132, 3567, 3968, 8327, 10598, 12465, 15875, 18895, 28611, 29418, 83693 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also numbers n such that (23*10^n+7)/3 is prime.

a(31) > 10^5. - Robert Price, Oct 08 2015

LINKS

Table of n, a(n) for n=1..30.

Makoto Kamada, Prime numbers of the form 766...669.

Index entries for primes involving repunits.

FORMULA

a(n) = A101150(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[(23*10^n + 7)/3], Print[n]], {n, 0, 10000}]

PROG

(PARI) for(n=1, 10^5, if(isprime((23*10^n+7)/3), print1(n", "))) \\ Altug Alkan, Oct 08 2015

CROSSREFS

Cf. A002275, A101150.

Sequence in context: A327018 A329128 A330442 * A281142 A110448 A005508

Adjacent sequences:  A103062 A103063 A103064 * A103066 A103067 A103068

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Jan 19 2005

EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

a(28)-a(29) from Kamada data by Robert Price, Dec 14 2010

a(30) from Robert Price, Oct 08 2015

STATUS

approved

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Last modified March 1 03:32 EST 2021. Contains 341732 sequences. (Running on oeis4.)