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A296094 Numbers k such that (43*10^k + 47)/9 is prime. 0
1, 3, 7, 12, 15, 21, 85, 177, 204, 477, 487, 1686, 2179, 2815, 2892, 3466, 7308, 17883, 25431, 69048, 89169, 126441 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
For k > 1, numbers such that the digit 4 followed by k-2 occurrences of the digit 7 followed by the digits 83 is prime (see Example section).
a(23) > 2*10^5.
LINKS
Makoto Kamada, Search for 47w83
EXAMPLE
3 is in this sequence because (43*10^3 + 47)/9 = 4783 is prime.
Initial terms and primes associated:
a(1) = 1, 53;
a(2) = 3, 4783;
a(3) = 7, 47777783;
a(4) = 12, 4777777777783;
a(5) = 15, 4777777777777783; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(43*10^# + 47)/9] &]
CROSSREFS
Sequence in context: A310234 A310235 A310236 * A075895 A033015 A225574
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Dec 04 2017
EXTENSIONS
a(22) from Robert Price, Dec 01 2018
STATUS
approved

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Last modified March 28 22:04 EDT 2024. Contains 371254 sequences. (Running on oeis4.)