OFFSET
1,2
COMMENTS
No term is divisible by 6 (A047253) because 7*1000000^k + 19 = 7*(76923*13 + 1)^k + 19 is divisible by 13 and is therefore not prime. - Bruno Berselli, Jul 05 2016
LINKS
Makoto Kamada, Search for 70w19.
EXAMPLE
3 is in this sequence because 7*10^3 + 19 = 7019 is prime.
5 is not in the sequence because 7*10^5 + 19 = 79*8861.
Initial terms and associated primes:
a(1) = 1: 89;
a(2) = 2: 719;
a(3) = 3: 7019;
a(4) = 4: 70019, etc.
MATHEMATICA
Select[Range[0, 3000], PrimeQ[7 10^# + 19] &]
PROG
(Magma) [n: n in [1..800] | IsPrime(7*10^n+19)];
(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime(7*10^n+19), print1(n, ", "))); \\ Altug Alkan, Jul 05 2016
(Python)
from sympy import isprime
def afind(limit, startk=0):
sevenpow10 = 7*10**startk
for k in range(startk, limit+1):
if isprime(sevenpow10 + 19):
print(k, end=", ")
k += 1
sevenpow10 *= 10
afind(500) # Michael S. Branicky, Dec 31 2021
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Vincenzo Librandi, Jul 04 2016
EXTENSIONS
a(20)-a(21) from Michael S. Branicky, Dec 31 2021
a(22)-a(23) from Kamada data by Tyler Busby, Apr 14 2024
STATUS
approved