A099412 0 together with numbers k such that 4*R_k - 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

0, 2, 4, 11, 28, 55, 94, 475, 2080, 4835, 5845, 12338, 20194, 49529, 56989, 71546, 77309

Offset

1,2

Comments

Also numbers k such that abs((4*10^k - 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