A103035 - OEIS

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A103035

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

1

0, 2, 5, 6, 11, 15, 69, 90, 134, 189, 245, 267, 270, 470, 1575, 2295, 2507, 3512, 3825, 6857, 11022, 11657, 17499, 35036, 41966, 50558, 93062

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OFFSET

1,2

COMMENTS

Also numbers n such that (58*10^n-13)/9 is prime.

a(28) > 10^5. - Robert Price, Sep 12 2015

LINKS

Table of n, a(n) for n=1..27.

Makoto Kamada, Prime numbers of the form 644...443.

Index entries for primes involving repunits.

FORMULA

a(n) = A101528(n-1) + 1 for n>1.

MATHEMATICA

Do[ If[ PrimeQ[(58*10^n - 13)/9], Print[n]], {n, 0, 10000}]

PROG

(PARI) is(n)=isprime(6*10^n + 4*(10^n-1)/9 - 1) \\ Anders Hellström, Sep 12 2015

CROSSREFS

Cf. A002275, A101528.

Sequence in context: A336527 A293398 A180323 * A088273 A049054 A319140

Adjacent sequences: A103032 A103033 A103034 * A103036 A103037 A103038

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Jan 18 2005

EXTENSIONS

a(21)-a(23) from Kamada data by Robert Price, Dec 14 2010

a(24)-a(25) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

Inserted a(1)=0 by Robert Price, Sep 12 2015

a(26)-a(27) from Robert Price, Sep 12 2015

STATUS

approved