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A292903
Numbers k such that (2*10^k + 547)/9 is prime.
0
0, 2, 3, 5, 15, 23, 24, 36, 45, 122, 168, 314, 390, 788, 818, 3588, 10502, 24467, 27356, 29955, 33074, 36669, 46776, 94604
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that k-2 occurrences of the digit 2 followed by the digits 83 is prime (see Example section).
a(25) > 2*10^5.
EXAMPLE
3 is in this sequence because (2*10^3 + 547)/9 = 283 is prime.
Initial terms and associated primes:
a(1) = 0, 61;
a(2) = 2, 83;
a(3) = 3, 283;
a(4) = 5, 22283;
a(5) = 15, 222222222222283; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(2*10^# + 547)/9] &]
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Oct 09 2017
STATUS
approved