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A267237 Numbers n such that 'n-1' prepended to 'n' n times yield primes. 1
7, 19, 989, 1187, 4183 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
a(5) produces the prime: 4182...[4183 times]4183 (16736 digits).
LINKS
EXAMPLE
7 occurs because '6' prepended 7 times to '7' produces prime (66666667).
MATHEMATICA
Select[ Range[1200], PrimeQ[ FromDigits[ StringJoin@@ ToString/@ PadLeft[{#}, #+1, #-1]]] &]
CROSSREFS
Cf. A267327.
Sequence in context: A359636 A330875 A330852 * A057866 A329001 A334982
KEYWORD
nonn,more,hard
AUTHOR
Mikk Heidemaa, Jan 12 2016
STATUS
approved

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Last modified May 23 21:14 EDT 2024. Contains 372765 sequences. (Running on oeis4.)