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 A104239 #10 Feb 16 2025 08:32:56
%S A104239 0,1,2,2,2,3,2,5,3,1,4,3,3,2,3,1,5,5,7,4,5,5,4,5,5,2,4,5,4,6,5,3,7,1,
%T A104239 4,4,3,4,3,6,5,7,5,7,8,4,7,7,1,6
%N A104239 Number of distinct prime factors of 135...(2n-1) (concatenation of n odd numbers).
%C A104239 Interestingly, 135791113151719 is prime.
%H A104239 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ConsecutiveNumberSequences.html">Consecutive Number sequences</a>
%e A104239 The number of distinct prime factors of 13 is 1 (a prime) - the second term in the sequence.
%e A104239 The number of distinct prime factors of 135 is 2 - the third term in the sequence.
%e A104239 The number of distinct prime factors of 1357 is 2 - the fourth term in the sequence.
%t A104239 Join[{0},Table[PrimeNu[FromDigits[Flatten[IntegerDigits/@Range[1,2n+1,2]]]],{n,50}]] (* _Harvey P. Dale_, Jun 15 2019 *)
%Y A104239 Cf. A001221, A048847.
%K A104239 nonn,base
%O A104239 1,3
%A A104239 _Parthasarathy Nambi_, Apr 16 2005
%E A104239 Corrected and extended by _Franklin T. Adams-Watters_, Sep 01 2006
%E A104239 Edited by _N. J. A. Sloane_, May 21 2008 at the suggestion of R. J. Mathar