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A274692
Numbers k such that 7*10^k + 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
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.
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
KEYWORD
nonn,more
AUTHOR
Robert Price, Jul 02 2016
STATUS
approved