A147555 - OEIS

%I #25 Jan 17 2019 13:44:08

%S 11,3,41,239,21649,53,2071723,1111111111111111111,

%T 11111111111111111111111,3191,2791,2028119,83,173,35121409,107,

%U 2559647034361,733,493121,241573142393627673576957439049,12171337159

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

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

%H Ray Chandler, <a href="/A147555/b147555.txt">Table of n, a(n) for n = 1..96</a>

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/repunit/">Factorizations of 11...11 (Repunit)</a>.

%F a(n) = A067063(A000040(n)) = A020639(A002275(A000040(n))) = A020639(A019328(A000040(n))). - _Ray Chandler_, May 11 2017

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

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

%K nonn

%O 1,1

%A _Farideh Firoozbakht_, Dec 26 2008

%E Edited by _Ray Chandler_, Apr 06 2011