A147556 Largest prime factor of prime(n)-th repunit number.

11, 37, 271, 4649, 513239, 265371653, 5363222357, 1111111111111111111, 11111111111111111111111, 77843839397, 57336415063790604359, 2212394296770203368013, 201763709900322803748657942361

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)=316362908763458525001406154038726382279.
		

Links

• Table of n, a(n) for n = 1..70
• Makoto Kamada, Factorizations of 11...11 (Repunit).

Crossrefs

Cf. A000040, A002275, A003020, A004022, A006530, A019328, A147555.

Programs

Mathematica

Table[FactorInteger[FromDigits[PadRight[{},n,1]]][[-1,1]],{n,Prime[ Range[15]]}] (* Harvey P. Dale, Feb 23 2016 *)

Formula

a(n) = A003020(A000040(n)) = A006530(A002275(A000040(n))) = A006530(A019328(A000040(n))). - Ray Chandler, May 11 2017

Extensions

Edited by Ray Chandler, Apr 06 2011

terms to a(66) in b-file from Ray Chandler, May 11 2017

a(67)-a(70) in b-file from Max Alekseyev, Apr 26 2022