login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

A266582
Numbers k such that (265*10^k - 7)/3 is prime.
0
1, 2, 4, 9, 13, 14, 16, 46, 99, 112, 116, 127, 146, 208, 512, 848, 1132, 2167, 2482, 2666, 3625, 14410, 16567, 21529, 26272, 69554, 69602
OFFSET
1,2
COMMENTS
For k > 0, numbers k such that the digits 88 followed by k-1 occurrences of the digit 3 followed by the digit 1 is prime (see Example section).
a(28) > 10^5.
EXAMPLE
4 is in this sequence because (265*10^4 - 7)/3 = 883331 is prime.
Initial terms and associated primes:
a(1) = 1, 881;
a(2) = 2, 8831;
a(3) = 4, 883331l
a(4) = 9, 88333333331;
a(5) = 13, 883333333333331, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(265*10^# - 7)/3] &]
PROG
(PARI) is(n)=ispseudoprime((265*10^n-7)/3) \\ Charles R Greathouse IV, Jun 13 2017
KEYWORD
nonn,more
AUTHOR
Robert Price, Jul 10 2016
STATUS
approved