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A099412 0 together with numbers n such that 4*R_n - 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 2
0, 2, 4, 11, 28, 55, 94, 475, 2080, 4835, 5845, 12338, 20194, 49529, 56989, 71546, 77309 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also numbers n such that abs((4*10^n-31))/9 is prime.

a(18) > 10^5. - Robert Price Sep 06 2014

LINKS

Table of n, a(n) for n=1..17.

Makoto Kamada, Prime numbers of the form 44...441.

Index entries for primes involving repunits

FORMULA

a(n) = A056681(n-1) + 1.

MATHEMATICA

Do[ If[ PrimeQ[ 4(10^n - 1)/9 - 3], Print[n]], {n, 0, 7000}]

PROG

(PARI)

for(n=0, 10^4, if(ispseudoprime(abs(4*(10^n-1)/9-3)), print1(n, ", "))) \\ Derek Orr, Sep 06 2014

CROSSREFS

Cf. A002275, A056681, A104659.

Sequence in context: A234844 A205504 A290337 * A100094 A099525 A024742

Adjacent sequences:  A099409 A099410 A099411 * A099413 A099414 A099415

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Oct 14 2004

EXTENSIONS

a(12)-a(17) from Kamada data by Robert Price, Sep 06 2014

STATUS

approved

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Last modified April 20 12:07 EDT 2021. Contains 343135 sequences. (Running on oeis4.)