A101395 Numbers k such that 4*10^k+7 is prime.
0, 1, 3, 9, 39, 2323
Offset: 1
Examples
n = 1, 3, 9 are members since 47, 4007 and 4000000007 are primes.
Links
- Makoto Kamada, Prime numbers of the form 400...007.
- Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.
- Index entries for primes involving repunits.
Programs
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Mathematica
Do[ If[ PrimeQ[4*10^n + 7], Print[n]], {n, 0, 10000}] -
PARI
is(n)=ispseudoprime(4*10^n+7) \\ Charles R Greathouse IV, Jun 12 2017
Formula
a(n) = A101714(n-1) + 1.
Comments