A275067 Numbers k such that 7*10^k + 39 is prime.

1, 2, 3, 4, 12, 19, 26, 32, 84, 164, 199, 251, 306, 510, 641, 1028, 1147, 1802, 1948, 2058, 2243, 2257, 4282, 7900, 7941, 10179, 10723, 13570, 20565, 29132, 34947, 63493, 87319, 107870, 183511, 183596, 209161, 227178, 273983, 287854

Offset

1,2

Comments

For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 0 followed by the digits 39 is prime (see Example section).

a(41) > 3*10^5.

Links

Table of n, a(n) for n=1..40.

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

Makoto Kamada, Search for 70w39.

Example

3 is in this sequence because 7*10^3 + 39 = 7039 is prime.
Initial terms and associated primes:
a(1) = 1, 109;
a(2) = 2, 739;
a(3) = 3, 7039;
a(4) = 4, 70000039;
a(5) = 12, 7000000000039, etc.

Mathematica

Select[Range[0, 100000], PrimeQ[7*10^# + 39] &]

Prog

(PARI) is(n)=ispseudoprime(7*10^n+39) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

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

Sequence in context: A048073 A002447 A331945 * A295620 A007499 A117555

Adjacent sequences: A275064 A275065 A275066 * A275068 A275069 A275070

Keyword

nonn,more

Author

Robert Price, Jul 15 2016

Extensions

a(34)-a(40) from Robert Price, Jul 02 2023

Status

approved