A274692 Numbers k such that 7*10^k + 43 is prime.

1, 2, 3, 7, 26, 27, 36, 44, 50, 57, 59, 73, 124, 152, 154, 250, 271, 301, 376, 451, 1177, 2299, 3740, 13159, 14780, 17435, 30098, 32521

Offset

1,2

Comments

For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 0 followed by the digits 43 is prime (see Example section).

a(29) > 10^5.

Links

Table of n, a(n) for n=1..28.

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

Makoto Kamada, Search for 70w43.

Example

3 is in this sequence because 7*10^3 + 43 = 7043 is prime.
Initial terms and associated primes:
a(1) = 1, 113;
a(2) = 2, 743;
a(3) = 3, 7043;
a(4) = 7, 70000043;
a(5) = 26, 700000000000000000000000043, etc.

Mathematica

Select[Range[0, 100000], PrimeQ[7*10^# + 43] &]

Prog

(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime(7*10^n + 43), print1(n, ", "))); \\ Altug Alkan, Jul 02 2016
(Magma) [n: n in [1..400] | IsPrime(7*10^n + 43)]; // Vincenzo Librandi, Jul 03 2016

Crossrefs

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

Sequence in context: A091230 A063852 A301519 * A342155 A308114 A092983

Adjacent sequences: A274689 A274690 A274691 * A274693 A274694 A274695

Keyword

nonn,more

Author

Robert Price, Jul 02 2016

Status

approved