A147555 Smallest prime factor of prime(n)-th repunit number.

11, 3, 41, 239, 21649, 53, 2071723, 1111111111111111111, 11111111111111111111111, 3191, 2791, 2028119, 83, 173, 35121409, 107, 2559647034361, 733, 493121, 241573142393627673576957439049, 12171337159

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..96

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

Formula

a(n) = A067063(A000040(n)) = A020639(A002275(A000040(n))) = A020639(A019328(A000040(n))). - Ray Chandler, May 11 2017

Example

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

Crossrefs

Cf. A000040, A002275, A004022, A019328, A020639, A067063, A147556.

Sequence in context: A102380 A204845 A260597 * A157883 A038317 A157781

Adjacent sequences: A147552 A147553 A147554 * A147556 A147557 A147558

Keyword

nonn

Author

Farideh Firoozbakht, Dec 26 2008

Extensions

Edited by Ray Chandler, Apr 06 2011

Status

approved