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A257038 Numbers k such that 9*R_(k+2) - 5*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length n. 0
3, 192, 1133, 4763, 5812, 48467, 130620, 466002 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Also, numbers k such that 95*10^n-1 is prime.

Terms from Kamada.

a(9) > 1170000.

LINKS

Table of n, a(n) for n=1..8.

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

Makoto Kamada, Prime numbers of the form 9499...99.

Index entries for primes involving repunits.

EXAMPLE

For k=3, 9*R_5 - 5*10^3 = 99999 - 5000 = 94999 which is prime.

MATHEMATICA

Select[Range[0, 1170000], PrimeQ[95*10^#-1 ] &]

PROG

(MAGMA) [n: n in [0..400] | IsPrime(95*10^n-1)]; // Vincenzo Librandi, Apr 15 2015

CROSSREFS

Cf. A002275.

Sequence in context: A261000 A032594 A159658 * A202109 A230171 A203749

Adjacent sequences:  A257035 A257036 A257037 * A257039 A257040 A257041

KEYWORD

more,hard,nonn

AUTHOR

Robert Price, Apr 14 2015

STATUS

approved

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Last modified November 18 04:44 EST 2019. Contains 329248 sequences. (Running on oeis4.)