

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
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OFFSET

1,2


COMMENTS

Also numbers n such that abs((4*10^n31))/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(n1) + 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^n1)/93)), 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



