A294636 Numbers k such that 9*10^k + 23 is prime.

1, 4, 10, 16, 22, 28, 49, 66, 67, 73, 89, 136, 198, 718, 2674, 3497, 7894, 9018, 12058, 16368, 91693

Offset

1,2

Comments

For k>1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 0 followed by the digits 23 is prime (see Example section).

a(22) > 2*10^5.

Links

Table of n, a(n) for n=1..21.

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

Makoto Kamada, Search for 90w23.

Example

4 is in this sequence because 9*10^4 + 23 = 90023 is prime.
Initial terms and associated primes:
a(1) = 1, 113;
a(2) = 4, 90023;
a(3) = 10, 90000000023;
a(4) = 16, 90000000000000023;
a(5) = 22, 90000000000000000000023; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[9*10^# + 23] &]

Crossrefs

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

Sequence in context: A269960 A016957 A109273 * A295560 A161644 A347652

Adjacent sequences: A294633 A294634 A294635 * A294637 A294638 A294639

Keyword

nonn,more,hard

Author

Robert Price, Nov 05 2017

Status

approved