This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A046420 #22 Feb 16 2025 08:32:39 %S A046420 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, %T A046420 69,71,73,74,79,83,85,86,89,93,94,97,101,103,106,109,113,115,118,119, %U A046420 129,134,137,139,141,142,146,149,151,157,159,163 %N A046420 Prime factors of repunit of length a(n) are all of different lengths. %H A046420 Max Alekseyev, <a href="/A046420/b046420.txt">Table of n, a(n) for n = 1..117</a> (first 107 terms from Ray Chandler) %H A046420 P. De Geest, <a href="https://www.worldofnumbers.com/repunits.htm">Repunits prime factors</a> %H A046420 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Repunit.html">Repunit</a> %e A046420 a(n)=14 -> 11*239*4649*909091 -> (2)(3)(4)(6) all of different lengths. %t A046420 Select[Range[60],Length[fi=FactorInteger[(10^#-1)/9]]== Plus@@Last/@fi==Length[Union[IntegerLength/@First/@fi]]&] (* _Ray Chandler_, Apr 24 2017 *) %Y A046420 Cf. A000042, A004022, A046053. %K A046420 nonn,base %O A046420 1,2 %A A046420 _Patrick De Geest_, Jul 15 1998 %E A046420 Offset changed to 1 and more terms added by _Ray Chandler_, Apr 24 2017