VOOZH about

URL: https://oeis.org/A293397

⇱ A293397 - OEIS

login
A293397
Numbers k such that 8*10^k + 87 is prime.
0
1, 2, 3, 6, 7, 8, 9, 21, 41, 51, 63, 67, 85, 174, 272, 297, 533, 697, 1326, 1344, 10668, 10814, 26252, 51721, 80342, 123657, 166227, 171296
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 0 followed by the digits 87 is prime (see Example section).
a(29) > 2*10^5.
EXAMPLE
3 is in this sequence because 8*10^3 + 87 = 887 is prime.
Initial terms and associated primes:
a(1) = 1, 167;
a(2) = 2, 887;
a(3) = 3, 8087;
a(4) = 6, 8000087;
a(5) = 7, 80000087; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[8*10^# + 87] &]
PROG
(PARI) isok(k) = isprime(8*10^k + 87); \\ Altug Alkan, Oct 08 2017
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 08 2017
EXTENSIONS
a(26)-a(28) from Robert Price, Oct 19 2019
STATUS
approved