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A102948 Numbers k such that 2*10^k + R_k + 2 is prime, where R_k = 11...1 is the repunit (A002275) of length k. 1
1, 3, 7, 13, 24, 30, 48, 52, 163, 175, 219, 228, 261, 754, 951, 1344, 1573, 3294, 3523, 14161, 70794 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also numbers k such that (19*10^k + 17)/9 is prime.

a(22) > 10^5. - Robert Price, Mar 04 2015

LINKS

Table of n, a(n) for n=1..21.

Makoto Kamada, Prime numbers of the form 211...113.

Index entries for primes involving repunits.

FORMULA

a(n) = A101953(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[(19*10^n + 17)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

Cf. A002275, A101953.

Sequence in context: A147380 A146606 A101302 * A232533 A061263 A156209

Adjacent sequences:  A102945 A102946 A102947 * A102949 A102950 A102951

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Dec 17 2004

EXTENSIONS

Addition of a(20) from Kamada data by Robert Price, Dec 09 2010

a(21) from Robert Price, Mar 04 2015

STATUS

approved

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Last modified June 25 17:46 EDT 2022. Contains 354851 sequences. (Running on oeis4.)