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A282810
Numbers k such that (26*10^k - 77)/3 is prime.
0
1, 3, 5, 7, 11, 12, 15, 27, 36, 108, 110, 115, 127, 155, 958, 2782, 3090, 6520, 9857, 14543, 21919, 23659, 24727, 49039, 92546, 114317, 131180, 146856, 204730, 219639, 238157
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 6 followed by the digits 41 is prime (see Example section).
a(32) > 3*10^5.
EXAMPLE
3 is in this sequence because (26*10^3 - 77)/3 = 8641 is prime.
Initial terms and associated primes:
a(1) = 1, 61;
a(2) = 3, 8641;
a(3) = 5, 866641;
a(4) = 7, 86666641;
a(5) = 11, 866666666641; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(26*10^# - 77)/3] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 22 2017
EXTENSIONS
a(26)-a(28) from Robert Price, Nov 15 2019
a(29)-a(31) from Robert Price, Jul 12 2023
STATUS
approved