A147556 - OEIS

A147556

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

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

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OFFSET

1,1

COMMENTS

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

LINKS

Table of n, a(n) for n = 1..70

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

FORMULA

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

EXAMPLE

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

MATHEMATICA

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

CROSSREFS

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

Sequence in context: A152094 A227412 A160623 * A201312 A120833 A261420

Adjacent sequences: A147553 A147554 A147555 * A147557 A147558 A147559

KEYWORD

nonn

AUTHOR

Farideh Firoozbakht, Dec 26 2008

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

STATUS

approved