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A103002 Numbers n such that 5*10^n - 7 is prime. 2
1, 3, 4, 8, 14, 16, 24, 61, 80, 87, 104, 108, 144, 2157, 3325, 4122, 20718, 51163, 140744 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also numbers n such that 4*10^n + 9*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

a(20) > 2*10^5. - Robert Price, Sep 15 2015

LINKS

Table of n, a(n) for n=1..19.

Makoto Kamada, Prime numbers of the form 499...993.

Index entries for primes involving repunits.

FORMULA

a(n) = A101739(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[5*10^n - 7], Print[n]], {n, 0, 10000}]

PROG

(PARI) is(n)=ispseudoprime(5*10^n-7) \\ Charles R Greathouse IV, Jun 06 2017

CROSSREFS

Cf. A002275, A108837, A101739.

Sequence in context: A049893 A307043 A218381 * A310012 A181408 A004979

Adjacent sequences:  A102999 A103000 A103001 * A103003 A103004 A103005

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Jan 17 2005

EXTENSIONS

Addition of a(17)-a(18) from Kamada data by Robert Price, Dec 10 2010

a(19) from Robert Price, Sep 15 2015

STATUS

approved

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Last modified June 6 11:14 EDT 2020. Contains 334827 sequences. (Running on oeis4.)