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

Author

Patrick De Geest, Jul 15 1998

Keywords

• nonn
• base

Examples

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

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

Crossrefs

Cf. A000042, A004022, A046053.

Programs

Mathematica

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

Extensions

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