A279793 Numbers k such that 4*10^k - 63 is prime.

2, 4, 5, 8, 9, 15, 19, 25, 26, 137, 141, 257, 399, 508, 524, 607, 709, 953, 989, 2484, 3196, 4538, 6448, 35401, 36106, 51530, 79327, 109316, 171891, 184004

Offset

1,1

Comments

For k>1, numbers such that the digit 3 followed by k-2 occurrences of the digit 9 followed by the digits 37 is prime (see Example section).

a(31) > 3*10^5.

Links

Table of n, a(n) for n=1..30.

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

Makoto Kamada, Search for 39w37.

Example

4 is in this sequence because 4*10^4 - 63 = 39937 is prime.
Initial terms and primes associated:
a(1) = 2, 337;
a(2) = 4, 39937;
a(3) = 5, 399937;
a(4) = 8, 399999937;
a(5) = 9, 3999999937; etc.

Mathematica

Select[Range[2, 100000], PrimeQ[4*10^# - 63] &]

Prog

(PARI) is(n)=ispseudoprime(4*10^n - 63) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

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

Sequence in context: A360772 A271392 A195364 * A305076 A332223 A269361

Adjacent sequences: A279790 A279791 A279792 * A279794 A279795 A279796

Keyword

nonn,more,hard

Author

Robert Price, Dec 18 2016

Extensions

a(28)-a(30) from Robert Price, Oct 24 2018

Status

approved