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

Author

Farideh Firoozbakht, Dec 26 2008

Keywords

• nonn

Comments

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

Examples

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

Links

• Ray Chandler, Table of n, a(n) for n = 1..96
• Makoto Kamada, Factorizations of 11...11 (Repunit).

Crossrefs

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

Formula

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

Extensions

Edited by Ray Chandler, Apr 06 2011