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 A116505 #19 Jul 07 2023 16:48:40
%S A116505 0,2,2,2,3,3,2,4,3,3,6,4,3,3,3,3,4,5,6,6,8,6,4,5,4,6,5,5,4,7,3,5,6,2,
%T A116505 7,5,4,4,6,8,5,7,4,4,9,7,5,7,6,9,3,3,4,9,5,4,6,4,4,6,3,7,4,9,6,8,3,7,
%U A116505 7,6,5,5,3,9,5,4,5,6,6,7,4,7,6,3,5,7,6,5,9,8,6,6,7,5,6,5,2,9,5,9
%N A116505 Number of distinct prime divisors of the concatenation of 1..n.
%C A116505 Dario Alpern's factorization program was used for n > 43.
%H A116505 Dario Alpern, <a href="https://www.alpertron.com.ar/ECM.HTM">Factorization using the Elliptic Curve Method</a>
%e A116505 123456 = 2*2*2*2*2*2*3*643, with distinct prime divisors 2, 3 and 643. Hence, a(6) = 3.
%t A116505 Table[PrimeNu[FromDigits[Flatten[IntegerDigits[Range[n]]]]], {n, 30}] (* _Jan Mangaldan_, Jul 07 2020 *)
%o A116505 (PARI) {a="";for(n=1,43,a=concat(a,n);print1(omega(eval(a)),", "))}
%Y A116505 Cf. A000422, A116504, A007908, A116505, A104759, A138789, A138790, A138793.
%K A116505 nonn,base
%O A116505 1,2
%A A116505 _Parthasarathy Nambi_, Mar 20 2006
%E A116505 Edited and extended by _Klaus Brockhaus_, Mar 29 2006
%E A116505 Terms 59-100 from _Sean A. Irvine_, Nov 04 2009