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A280019
Numbers k such that (94*10^k + 11)/3 is prime.
0
1, 2, 3, 5, 10, 23, 29, 56, 68, 199, 364, 436, 478, 1178, 1187, 1869, 4733, 11816, 11867, 17383, 27987, 42005, 51889, 111770, 113176, 168541
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digits 31 followed by k-1 occurrences of the digit 3 followed by the digit 7 is prime (see Example section).
a(27) > 2*10^5.
EXAMPLE
3 is in this sequence because (94*10^3 + 11)/3 = 31337 is prime.
Initial terms and associated primes:
a(1) = 1, 317;
a(2) = 2, 3137;
a(3) = 3, 31337;
a(4) = 5, 3133337;
a(5) = 10, 313333333337; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(94*10^# + 11)/3] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Feb 21 2017
EXTENSIONS
a(24)-a(26) from Robert Price, Apr 03 2020
STATUS
approved