A284741 Numbers k such that (29*10^k + 259)/9 is prime.

1, 3, 4, 6, 9, 10, 24, 27, 66, 76, 136, 346, 399, 978, 1228, 2227, 4005, 5916, 6394, 7438, 18934, 20020, 31866, 85438

Offset

1,2

Comments

For k>1, numbers such that the digit 3 followed by k-2 occurrences of the digit 2 followed by the digits 51 is prime (see Example section).

a(25) > 2*10^5.

Links

Table of n, a(n) for n=1..24.

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

Makoto Kamada, Search for 32w51.

Example

3 is in this sequence because (29*10^3 + 259)/9 = 3251 is prime.
Initial terms and primes associated:
a(1) = 1, 61;
a(2) = 3, 3251;
a(3) = 4, 32251;
a(4) = 6, 3222251;
a(5) = 9, 3222222251; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(29*10^# + 259)/9] &]

Crossrefs

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

Sequence in context: A268110 A124093 A025061 * A342577 A037969 A329862

Adjacent sequences: A284738 A284739 A284740 * A284742 A284743 A284744

Keyword

nonn,more,hard

Author

Robert Price, Apr 01 2017

Status

approved