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A099414 Numbers n such that 4*R_n + 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 2
0, 3, 5, 6, 48, 108, 245, 1044, 20208, 52740, 89189 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also numbers n such that (4*10^n+41)/9 is prime.

a(12) > 10^5. - Robert Price, Nov 09 2014

LINKS

Table of n, a(n) for n=1..11.

Makoto Kamada, Prime numbers of the form 44...449.

Index entries for primes involving repunits

FORMULA

a(n) = A056683(n-1) + 1.

MATHEMATICA

Do[ If[ PrimeQ[ 4(10^n - 1)/9 + 5], Print[n]], {n, 5000}]

PROG

(MAGMA) [n: n in [0..300] | IsPrime((4*10^n+41) div 9)]; // Vincenzo Librandi Nov 10 2014

CROSSREFS

Cf. A002275, A056683.

Sequence in context: A086189 A137082 A242501 * A004785 A099744 A024601

Adjacent sequences:  A099411 A099412 A099413 * A099415 A099416 A099417

KEYWORD

nonn,more

AUTHOR

Robert G. Wilson v, Oct 14 2004

EXTENSIONS

a(9)-a(11) from Robert Price, Nov 09 2014

STATUS

approved

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Last modified April 11 05:30 EDT 2021. Contains 342886 sequences. (Running on oeis4.)