A295401 Numbers k such that 3*10^k + 97 is prime.

1, 2, 4, 14, 19, 22, 87, 141, 228, 274, 441, 514, 721, 1674, 1710, 2725, 2858, 4658, 19862, 20175, 25474, 30309, 34740

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 97 is prime (see Example section).

a(24) > 2*10^5.

Links

Table of n, a(n) for n=1..23.

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

Makoto Kamada, Search for 30w97

Example

2 is in this sequence because 3*10^2 + 97 = 397 is prime.
Initial terms and primes associated:
a(1) = 1, 127;
a(2) = 2, 397;
a(3) = 4, 30097;
a(4) = 14, 300000000000097;
a(5) = 19, 30000000000000000097; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[3*10^# + 97] &]

Prog

(PARI) isok(k) = isprime(3*10^k + 97); \\ Michel Marcus, Nov 22 2017

Crossrefs

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

Sequence in context: A253444 A336821 A299488 * A342605 A032398 A245764

Adjacent sequences: A295398 A295399 A295400 * A295402 A295403 A295404

Keyword

nonn,more,hard,changed

Author

Robert Price, Nov 21 2017

Status

approved