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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

Table of n, a(n) for n=1..5.

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: A335990 A330875 A330852 * A057866 A329001 A334982

Adjacent sequences:  A267234 A267235 A267236 * A267238 A267239 A267240

KEYWORD

nonn,more,hard

AUTHOR

Mikk Heidemaa, Jan 12 2016

STATUS

approved

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Last modified August 8 11:12 EDT 2020. Contains 336293 sequences. (Running on oeis4.)