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A274692 Numbers n such that 7*10^n + 43 is prime. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For n>1, numbers n such that the digit 7 followed by n-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 * A308114 A092983 A089708

Adjacent sequences:  A274689 A274690 A274691 * A274693 A274694 A274695

KEYWORD

nonn,more

AUTHOR

Robert Price, Jul 02 2016

STATUS

approved

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Last modified June 26 10:12 EDT 2019. Contains 324375 sequences. (Running on oeis4.)