A281645 Numbers k such that 4*10^k + 79 is prime.

0, 2, 3, 6, 8, 24, 36, 38, 45, 47, 57, 68, 69, 125, 672, 690, 999, 1199, 3512, 4013, 4208, 12042, 18492, 21945, 31158, 43430, 48548, 117123

Offset

1,2

Comments

For k>1, numbers such that the digit 4 followed by k-2 occurrences of the digit 0 followed by the digits 79 is prime (see Example section).

a(29) > 2*10^5.

Links

Table of n, a(n) for n=1..28.

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

Makoto Kamada, Search for 40w79.

Example

3 is in this sequence because 4*10^3 + 79 = 4079 is prime.
Initial terms and primes associated:
a(1) = 0, 83;
a(2) = 2, 479;
a(3) = 3, 4079;
a(4) = 6, 4000079;
a(5) = 8, 400000079; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[4*10^# + 79] &]

Crossrefs

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

Sequence in context: A153915 A355581 A093705 * A351853 A224211 A187026

Adjacent sequences: A281642 A281643 A281644 * A281646 A281647 A281648

Keyword

nonn,more,hard

Author

Robert Price, Jan 25 2017

Extensions

a(28) from Robert Price, Aug 10 2018

Status

approved