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A111471 a(1) = 1; for n>1, a(n) = least k such that concatenation of n copies of k with all previous concatenations gives a prime. 8
1, 9, 7, 3, 29, 19, 21, 121, 7, 211, 207, 11, 221, 347, 99, 123, 303, 189, 1131, 1179, 2069, 3437, 2211, 211, 3169, 1551, 3493, 7433, 6939, 1053, 1537, 9417, 4491, 1257, 19693, 9, 1653, 3329, 317, 8667, 799, 1053, 5617, 6049, 1721, 24871, 2751, 737, 3303, 29079 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..50.

EXAMPLE

199, 199777, 1997773333, 19977733332929292929 are all primes.

CROSSREFS

Cf. A111472.

Sequence in context: A081821 A164102 A105532 * A078527 A092425 A019647

Adjacent sequences:  A111468 A111469 A111470 * A111472 A111473 A111474

KEYWORD

base,nonn

AUTHOR

Amarnath Murthy, Aug 05 2005

EXTENSIONS

More terms from Donovan Johnson, Feb 26 2008

STATUS

approved

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Last modified November 13 10:50 EST 2019. Contains 329093 sequences. (Running on oeis4.)