A239586 - OEIS

A239586

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

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, 31, 37, 23, 41, 43, 37, 29, 47, 31, 23, 41, 29, 43, 53, 31, 47, 37, 59, 29, 61, 53, 41, 37, 31, 43, 67, 59, 41, 71, 61, 47, 73, 43, 29, 37, 79, 67, 47, 31, 53, 83

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

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

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

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..20000

Dario Alpern, Brilliant Numbers

EXAMPLE

See A239585.

MATHEMATICA

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 *)

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 *)

Map[FactorInteger[#][[-1, 1]]&, Flatten[Array[dlist2, 2]]] (* Paolo Xausa, Oct 08 2024 *)

PROG

(Haskell)

a239586 n = a078972 n `div` a239585 n

CROSSREFS

Subsequence of A084127.

Cf. A006530, A055642, A078972, A239585.

Sequence in context: A122444 A373751 A066072 * A180611 A084127 A377214

Adjacent sequences: A239583 A239584 A239585 * A239587 A239588 A239589

KEYWORD

nonn,look,base

AUTHOR

Reinhard Zumkeller, Mar 22 2014

STATUS

approved