A239586 - OEIS

%I #18 Oct 10 2024 15:29:52

%S 2,3,3,5,7,5,7,5,7,7,11,13,13,17,19,17,19,23,17,23,29,19,31,19,29,23,

%T 31,37,23,41,43,37,29,47,31,23,41,29,43,53,31,47,37,59,29,61,53,41,37,

%U 31,43,67,59,41,71,61,47,73,43,29,37,79,67,47,31,53,83

%N Prime factor >= other prime factor of n-th brilliant number, cf. A078972.

%C a(n) = A006530(A078972(n)) = A078972(n) / A239585(n).

%C A055642(a(n)) = A055642(A239585(n)).

%H Reinhard Zumkeller, <a href="/A239586/b239586.txt">Table of n, a(n) for n = 1..20000</a>

%H Dario Alpern, <a href="https://www.alpertron.com.ar/BRILLIANT.HTM">Brilliant Numbers</a>

%e See A239585.

%t Table[With[{f = FactorInteger[k]}, If[Total[f[[All, 2]]] == 2 && Length[Union[IntegerLength[f[[All, 1]]]]] == 1, f[[-1, 1]], Nothing]], {k, 1000}] (* _Paolo Xausa_, Oct 02 2024 *)

%t dlist2[d_] := Union[Times @@@ Tuples[Prime[Range[PrimePi[10^(d-1)] + 1, PrimePi[10^d]]], 2]]; (* Generates terms with d-digits prime factors -- faster but memory intensive *)

%t Map[FactorInteger[#][[-1,1]]&,Flatten[Array[dlist2,2]]] (* _Paolo Xausa_, Oct 08 2024 *)

%o (Haskell)

%o a239586 n = a078972 n `div` a239585 n

%Y Subsequence of A084127.

%Y Cf. A006530, A055642, A078972, A239585.

%K nonn,look,base

%O 1,1

%A _Reinhard Zumkeller_, Mar 22 2014