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A101396 Numbers n such that 4*10^n - 9 is prime. 1
1, 17, 19, 29, 43, 119, 173, 949, 1609, 5579, 19679, 34147, 43493, 97799 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(15) > 10^5. - Robert Price, Mar 17 2015

All terms are odd, since 4 * 10^(2*k) - 9 = (2 * 10^k - 3)*(2 * 10^k + 3). - Robert Israel, Mar 17 2015

LINKS

Table of n, a(n) for n=1..14.

Makoto Kamada, Prime numbers of the form 399...991.

Index entries for primes involving repunits.

FORMULA

a(n) = A101848(n) + 1.

EXAMPLE

n = 1, 17, 19 are members since 31, 399999999999999991 and 39999999999999999991 are primes.

MAPLE

select(n -> n::odd and isprime(4*10^n-9), [$1..10000]); # Robert Israel, Mar 17 2015

MATHEMATICA

Do[ If[ PrimeQ[4*10^n - 9], Print[n]], {n, 0, 10000}]

PROG

(MAGMA) [n: n in [1..300] |IsPrime(4*10^n - 9)]; // Vincenzo Librandi, Mar 18 2015

(PARI) is(n)=ispseudoprime(4*10^n-9) \\ Charles R Greathouse IV, Jun 12 2017

CROSSREFS

Cf. A095714, A101848.

Sequence in context: A038969 A065742 A155089 * A050266 A045803 A098933

Adjacent sequences:  A101393 A101394 A101395 * A101397 A101398 A101399

KEYWORD

more,nonn

AUTHOR

Julien Peter Benney (jpbenney(AT)ftml.net), Jan 15 2005

EXTENSIONS

a(11) from Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

a(12)-a(14) from Kamada data by Robert Price, Mar 17 2015

STATUS

approved

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Last modified April 25 13:31 EDT 2019. Contains 322461 sequences. (Running on oeis4.)