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A116504 Number of distinct prime divisors of the concatenation of n,...,1.

%I A116504 #20 Nov 02 2024 09:13:21
%S A116504 0,2,2,2,3,2,2,3,3,3,2,3,3,4,5,4,6,8,4,5,4,5,4,5,6,7,5,5,7,8,3,6,5,7,
%T A116504 8,6,4,3,6,5,8,6,3,7,6,5,7,7,3,6,3,7,9,9,3,4,4,6,3,3,5,8,5,6,7,7,4,8,
%U A116504 8,4,8,4,7,8,10,3,7,6,4,7,7,1,3,8,3,8,5,4,5,7,11,9,6
%N A116504 Number of distinct prime divisors of the concatenation of n,...,1.
%H A116504 Sean A. Irvine, <a href="/A116504/b116504.txt">Table of n, a(n) for n = 1..106</a>
%e A116504 87654321 = 3*3*1997*4877, distinct prime divisors are 3, 1997 and 4877, hence a(8) = 3.
%t A116504 b = {}; a = {}; Do[w = RealDigits[n]; w = First[w]; Do[PrependTo[a, w[[Length[w] - k + 1]]], {k, 1, Length[w]}]; p = FromDigits[a]; m = FactorInteger[p]; AppendTo[b, Length[m]], {n, 1, 30}]; b (* _Artur Jasinski_, Mar 30 2008 *)
%t A116504 Table[PrimeNu[FromDigits[Flatten[IntegerDigits/@Range[n,1,-1]]]],{n,95}] (* _Harvey P. Dale_, Oct 03 2015 *)
%o A116504 (PARI) {a="";for(n=1,58,a=concat(n,a);print1(omega(eval(a)),","))}
%Y A116504 Cf. A116505.
%Y A116504 Cf. A000422, A116504, A007908, A116505, A104759, A138789, A138790, A138793.
%K A116504 nonn,base
%O A116504 1,2
%A A116504 _Parthasarathy Nambi_, Mar 20 2006
%E A116504 Edited and extended by _Klaus Brockhaus_, Mar 29 2006
%E A116504 Terms a(59)-a(93) from _Sean A. Irvine_, Nov 04 2009
%E A116504 a(90) corrected by _Sean A. Irvine_, Nov 02 2024