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A295401 Numbers k such that 3*10^k + 97 is prime. 0
1, 2, 4, 14, 19, 22, 87, 141, 228, 274, 441, 514, 721, 2725, 2858, 4658, 19862, 20175, 25474, 1674, 1710, 30309, 34740 (list; graph; refs; listen; history; text; internal format)
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: A077570 A253444 A299488 * A032398 A245764 A032309

Adjacent sequences:  A295398 A295399 A295400 * A295402 A295403 A295404

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Nov 21 2017

STATUS

approved

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Last modified November 14 12:38 EST 2019. Contains 329114 sequences. (Running on oeis4.)