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A147555 Smallest prime factor of prime(n)-th repunit number. 2
11, 3, 41, 239, 21649, 53, 2071723, 1111111111111111111, 11111111111111111111111, 3191, 2791, 2028119, 83, 173, 35121409, 107, 2559647034361, 733, 493121, 241573142393627673576957439049, 12171337159 (list; graph; refs; listen; history; internal format)
OFFSET

1,1

COMMENTS

The sequence of repunit primes is a subsequence of this sequence.

LINKS

Ray Chandler, Table of n, a(n) for n = 1..58

Makoto Kamada, Factorizations of 11...11 (Repunit).

FORMULA

a(n) = A020639(A002275(A000040(n))) = A020639(A019328(A000040(n))).

EXAMPLE

prime(15)=47 and (10^47-1)/9 = 35121409*316362908763458525001406154038726382279, so a(15)=35121409.

CROSSREFS

Cf. A004022, A147556.

Sequence in context: A087100 A102380 A204845 * A157883 A038317 A157781

Adjacent sequences:  A147552 A147553 A147554 * A147556 A147557 A147558

KEYWORD

nonn

AUTHOR

Farideh Firoozbakht (mymontain(AT)yahoo.com), Dec 26 2008

EXTENSIONS

Edited by Ray Chandler (rayjchandler(AT)sbcglobal.net), Apr 06 2011

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Last modified February 17 02:48 EST 2012. Contains 205978 sequences.