A046420 Prime factors of repunit of length a(n) are all of different lengths.

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

Offset

1,2

Links

Max Alekseyev, Table of n, a(n) for n = 1..117 (first 107 terms from Ray Chandler)

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: A003037 A347983 A259466 * A108318 A358876 A006456

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