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A295329
Numbers k such that (28*10^k + 359)/9 is prime.
0
0, 1, 4, 6, 9, 10, 24, 94, 136, 144, 186, 337, 390, 448, 564, 916, 1384, 2052, 5424, 28636, 39574, 65532
OFFSET
1,3
COMMENTS
For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 1 followed by the digits 51 is prime (see Example section).
a(23) > 2*10^5.
EXAMPLE
1 is in this sequence because (28*10^1 + 359)/9 = 71 is prime.
Initial terms and associated primes:
a(1) = 0, 43;
a(2) = 1, 71;
a(3) = 4, 31151;
a(4) = 6, 3111151;
a(5) = 9, 3111111151; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(28*10^# + 359)/9] &]
PROG
(PARI) isok(k) = isprime((28*10^k + 359)/9); \\ Michel Marcus, Nov 20 2017
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Nov 19 2017
STATUS
approved