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A291611 Numbers k such that 5*10^k + 81 is prime. 1
1, 3, 6, 16, 30, 33, 36, 37, 85, 288, 561, 805, 850, 1057, 1192, 1312, 2571, 4579, 5223, 5940, 10191, 18756, 24564, 29595, 43891, 65905, 89118, 97963, 112003, 139945, 174101, 195221 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
For k>1, numbers such that the digit 5 followed by k-2 occurrences of the digit 0 followed by the digits 81 is prime (see Example section).
a(33) > 2*10^5.
LINKS
Makoto Kamada, Search for 50w81
EXAMPLE
3 is in this sequence because 5*10^3 + 81 = 5081 is prime.
Initial terms and primes associated:
a(1) = 1, 131;
a(2) = 3, 5081;
a(3) = 6, 5000081;
a(4) = 16, 50000000000000081;
a(5) = 30, 5000000000000000000000000000081; etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[5*10^# + 81] &]
CROSSREFS
Sequence in context: A032247 A052281 A295062 * A308401 A196261 A229180
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Aug 27 2017
EXTENSIONS
a(29)-a(32) from Robert Price, Mar 04 2019
Terms reordered into ascending order by Robert Price, Apr 03 2022
STATUS
approved

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Last modified March 28 05:39 EDT 2024. Contains 371235 sequences. (Running on oeis4.)