A288821 Numbers k such that 10^k - 401 is prime.

3, 6, 9, 11, 12, 25, 47, 166, 222, 234, 352, 407, 515, 646, 1161, 2475, 4329, 7191, 12894, 16007, 25819, 67579, 88457, 117135

Offset

1,1

Comments

For k > 2, numbers k such that k-3 occurrences of the digit 9 followed by the digits 599 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 9w599.

Example

6 is in this sequence because 10^6 - 401 = 999599 is prime.
Initial terms and associated primes:
a(1) = 3, 599;
a(2) = 6, 999599;
a(3) = 9, 999999599;
a(4) = 11, 99999999599;
a(5) = 12, 999999999599; etc.

Mathematica

Select[Range[3, 100000], PrimeQ[10^# - 401] &]

Crossrefs

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

Sequence in context: A086883 A154777 A338432 * A343306 A267881 A310142

Adjacent sequences: A288818 A288819 A288820 * A288822 A288823 A288824

Keyword

nonn,more,hard

Author

Robert Price, Jun 17 2017

Extensions

a(24) from Robert Price, Jan 19 2018

Status

approved