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A256326 Numbers k such that 3*R_(k+2) - 2*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length n. 0
0, 1, 3, 4, 6, 70, 73, 109, 237, 264, 337, 496, 1029, 1077, 1254, 1288, 2049, 3606, 5035, 9163, 35899 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Also, numbers k such that (94*10^n-1)/3  is prime.

Terms from Kamada.

a(22) > 250000.

LINKS

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

Makoto Kamada, Near-repdigit numbers of the form ABAA...AA.

Makoto Kamada, Prime numbers of the form 3133...33.

Index entries for primes involving repunits.

EXAMPLE

For k=3, 3*R_5 - 2*10^3 = 33333 - 2000 = 31333 which is prime.

MATHEMATICA

Select[Range[0, 250000], PrimeQ[(94*10^#-1)/3 ] &]

CROSSREFS

Cf. A002275.

Sequence in context: A019209 A019120 A263940 * A239244 A267943 A066466

Adjacent sequences:  A256323 A256324 A256325 * A256327 A256328 A256329

KEYWORD

more,hard,nonn

AUTHOR

Robert Price, Apr 14 2015

STATUS

approved

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Last modified July 2 16:14 EDT 2020. Contains 335404 sequences. (Running on oeis4.)