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A046420 Prime factors of repunit of length a(n) are all of different lengths. 1
1, 2, 3, 4, 5, 7, 11, 14, 17, 19, 23, 31, 34, 37, 38, 41, 43, 47, 49, 51, 53, 57, 59, 62, 67, 69, 71, 73, 74, 79, 83, 85, 86, 89, 93, 94, 97, 101, 103, 106, 109, 113, 115, 118, 119, 129, 134, 137, 139, 141, 142, 146, 149, 151, 157, 159, 163 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Ray Chandler, Table of n, a(n) for n = 1..107

P. De Geest, Repunits prime factors

Eric Weisstein's World of Mathematics, Repunit

EXAMPLE

a(n)=14 -> 11*239*4649*909091 -> (2)(3)(4)(6) all of different lengths.

MATHEMATICA

Select[Range[60], Length[fi=FactorInteger[(10^#-1)/9]]== Plus@@Last/@fi==Length[Union[IntegerLength/@First/@fi]]&] (* Ray Chandler, Apr 24 2017 *)

CROSSREFS

Cf. A000042, A004022, A046053.

Sequence in context: A192586 A003037 A259466 * A108318 A006456 A018134

Adjacent sequences:  A046417 A046418 A046419 * A046421 A046422 A046423

KEYWORD

nonn,base

AUTHOR

Patrick De Geest, Jul 15 1998

EXTENSIONS

Offset changed to 1 and more terms added by Ray Chandler, Apr 24 2017

STATUS

approved

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Last modified January 23 07:07 EST 2020. Contains 331168 sequences. (Running on oeis4.)