login
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
OFFSET
1,1
COMMENTS
The sequence of repunit primes is a subsequence of this sequence.
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.
KEYWORD
nonn
AUTHOR
Farideh Firoozbakht, Dec 26 2008
EXTENSIONS
Edited by Ray Chandler, Apr 06 2011
STATUS
approved