

A282571


Numbers k such that 2*10^k  27 is prime.


0



2, 3, 4, 9, 26, 40, 41, 56, 82, 114, 150, 155, 203, 213, 578, 2638, 4761, 10202, 14211, 16421, 18047, 30701, 53834, 66826, 115784, 141407
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OFFSET

1,1


COMMENTS

For k>1, numbers such that the digit 1 followed by k2 occurrences of the digit 9 followed by the digits 73 is prime (see Example section).
a(27) > 2*10^5.


LINKS

Table of n, a(n) for n=1..26.
Makoto Kamada, Factorization of nearrepdigitrelated numbers.
Makoto Kamada, Search for 19w73.


EXAMPLE

3 is in this sequence because 2*10^3  27 = 1973 is prime.
Initial terms and primes associated:
a(1) = 2, 173;
a(2) = 3, 1973;
a(3) = 4, 19973;
a(4) = 9, 1999999973;
a(5) = 26, 199999999999999999999999973; etc.


MATHEMATICA

Select[Range[2, 100000], PrimeQ[2*10^#  27] &]


PROG

(PARI) isok(k) = isprime(2*10^k  27); \\ Michel Marcus, Feb 19 2017


CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
Sequence in context: A085612 A073915 A076381 * A063455 A001144 A121253
Adjacent sequences: A282568 A282569 A282570 * A282572 A282573 A282574


KEYWORD

nonn,more,hard


AUTHOR

Robert Price, Feb 18 2017


EXTENSIONS

a(25)a(26) from Robert Price, May 05 2018


STATUS

approved



