A275522 Numbers k such that (28*10^k + 773)/9 is prime.

0, 2, 5, 6, 11, 20, 32, 59, 81, 98, 128, 437, 758, 989, 998, 1403, 1548, 1907, 1914, 2219, 5414, 9047, 13196, 18518, 28382

Offset: 1

Author

Robert Price, Jul 31 2016

Keywords

• nonn
• more

Comments

For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 1 followed by the digits 97 is prime (see Example section).

a(26) > 10^5.

Examples

			5 is in this sequence because (28*10^5 + 773)/9 = 311197 is prime.
Initial terms and associated primes:
a(1) = 0, 89;
a(2) = 2, 397;
a(3) = 5, 311197;
a(4) = 6, 3111197;
a(5) = 11, 311111111197, etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.
• Makoto Kamada, Search for 31w97.

Crossrefs

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

Programs

Magma

[n: n in [0..500] | IsPrime((28*10^n+773) div 9)]; // Vincenzo Librandi, Aug 01 2016

Mathematica

Select[Range[0, 100000], PrimeQ[(28*10^# + 773)/9] &]

PARI

is(n)=ispseudoprime((28*10^n+773)/9) \\ Charles R Greathouse IV, Jun 13 2017