A057736
Primes p such that 2^p + 3 is prime.
Original entry on oeis.org
- J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 67, p. 24, Ellipses, Paris 2008.
Cf.
A057737 (the corresponding primes).
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Select[Prime[Range[20]],PrimeQ[2^#+3]&] (* Harvey P. Dale, Jun 06 2022 *)
-
from sympy import isprime, primerange
def afind(limit):
for p in primerange(2, limit+1):
if isprime(2**p + 3): print(p, end=", ")
afind(1000) # Michael S. Branicky, Mar 07 2021
A142247
Primes of the form 2^p - 1, 2^p + 1, 2^p - 3, or 2^p + 3, where p is prime.
Original entry on oeis.org
3, 5, 7, 11, 29, 31, 127, 131, 8191, 131071, 524287, 536870909, 2147483647, 2305843009213693951, 147573952589676412931, 618970019642690137449562111, 162259276829213363391578010288127
Offset: 1
-
f[n_] := If[PrimeQ[2^Prime[n] - 1] || PrimeQ[2^Prime[n] + 1] || PrimeQ[2^Prime[n] - 3] || PrimeQ[2^Prime[n] + 3], {2^Prime[n] - 1, 2^Prime[n] + 1, 2^Prime[n] - 3, 2^Prime[n] + 3}, {}]; a = Flatten[Table[f[n], {n, 1, 100}]]; Union[Flatten[Table[If[PrimeQ[a[[n]]], a[[n]], {}], {n, 1, Length[a]}]]]
Showing 1-2 of 2 results.
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