A274676 Numbers k such that 7*10^k + 13 is prime.
1, 3, 9, 12, 18, 19, 36, 37, 49, 67, 337, 893, 1924, 8044, 11610, 13560, 18777, 35376, 53601, 56022, 66488, 89801, 190210
Offset: 1
Examples
3 is in this sequence because 7*10^3 + 13 = 7013 is prime. 4 is not in the sequence because 7*10^4 + 13 = 70013 = 53 * 1321. Initial terms and associated primes: a(1) = 1: 83; a(2) = 3: 7013; a(3) = 9: 7000000013; a(4) = 12: 7000000000013, etc.
Links
- Makoto Kamada, Search for 70w13.
Crossrefs
Programs
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Magma
[n: n in [1..800] | IsPrime(7*10^n+13)];
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Maple
select(t -> isprime(7*10^t+13), [$1..2000]); # Robert Israel, Jul 03 2016
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Mathematica
Select[Range[0, 3000], PrimeQ[7 * 10^# + 13] &]
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PARI
is(n) = ispseudoprime(7*10^n+13) \\ Felix Fröhlich, Jul 03 2016
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PARI
lista(nn) = for(n=1, nn, if(ispseudoprime(7*10^n+13), print1(n, ", "))); \\ Altug Alkan, Jul 03 2016
Extensions
a(15) from Michael S. Branicky, Jan 22 2023
a(16)-a(17) from Michael S. Branicky, Apr 10 2023
a(18)-a(23) from Kamada data by Tyler Busby, Apr 15 2024
Comments