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A271360 Numbers k such that 5*10^k + 87 is prime. 0
1, 2, 3, 4, 6, 16, 38, 39, 46, 61, 62, 100, 116, 152, 190, 298, 472, 642, 688, 1676, 1971, 2338, 4389, 4520, 4986, 7765, 9428, 10820, 18984, 19797, 35360, 42146, 168807 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k>1, numbers such that the digit 5 followed by k-2 occurrences of the digit 0 followed by the digits 87 is prime (see Example section).

a(34) > 2*10^5.

LINKS

Table of n, a(n) for n=1..33.

Makoto Kamada, Search for 50w87.

EXAMPLE

3 is in this sequence because 5*10^3 + 87 = 5087 is prime.

Initial terms and primes associated:

a(1) = 1, 137;

a(2) = 2, 587;

a(3) = 3, 5087;

a(4) = 4, 50087;

a(5) = 6, 5000087, etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[5*10^# + 87] &]

PROG

(PARI) is(n)=ispseudoprime(5*10^n + 87) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.

Sequence in context: A102946 A026094 A285191 * A236413 A069860 A084391

Adjacent sequences:  A271357 A271358 A271359 * A271361 A271362 A271363

KEYWORD

nonn,more

AUTHOR

Robert Price, Apr 05 2016

EXTENSIONS

a(33) from Robert Price, Feb 24 2019

STATUS

approved

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Last modified November 13 02:59 EST 2019. Contains 329085 sequences. (Running on oeis4.)