A293826 Numbers k such that 3*10^k + 77 is prime.

1, 6, 9, 10, 11, 16, 17, 21, 108, 180, 324, 340, 606, 700, 1857, 2447, 2658, 11055, 16177, 16439, 18767, 33173, 47842, 105582, 107389

Offset

1,2

Comments

For k>1, numbers such that the digit 3 followed by k-2 occurrences of the digit 0 followed by the digits 77 is prime (see Example section).

a(26) > 2*10^5.

Links

Table of n, a(n) for n=1..25.

Makoto Kamada, Factorization of near-repdigit-related numbers.

Makoto Kamada, Search for 30w77

Example

6 is in this sequence because 3*10^6 + 77 = 3000077 is prime.
Initial terms and primes associated:
a(1) = 1, 107;
a(2) = 6, 3000077;
a(3) = 9, 3000000077;
a(4) = 10, 30000000077;
a(5) = 11, 300000000077; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[3*10^# + 77] &] (* Corrected by Georg Fischer, Jul 22 2019 *)

Crossrefs

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

Sequence in context: A124257 A066385 A226913 * A103092 A337940 A104523

Adjacent sequences: A293823 A293824 A293825 * A293827 A293828 A293829

Keyword

nonn,more,hard

Author

Robert Price, Oct 16 2017

Extensions

a(24)-a(25) from Robert Price, Sep 01 2018

Status

approved