OFFSET
1,6
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..16384
FORMULA
MATHEMATICA
ffi[x_] := Flatten[FactorInteger[x]]; lf[x_] := Length[FactorInteger[x]]; ba[x_] := Table[Part[ffi[x], 2*w-1], {w, 1, lf[x]}]; f1[x_] := n; f2[x_] := DivisorSigma[2, x]; Table[Min[Intersection[ba[f1[w]], ba[f2[w]]]], {w, 1, 128}]
(* Second program: *)
Array[If[CoprimeQ[#1, #2], 1, Min@ Apply[Intersection, Map[FactorInteger[#][[All, 1]] &, {#1, #2}]]] & @@ {#, DivisorSigma[2, #]} &, 105] (* Michael De Vlieger, Nov 03 2017 *)
PROG
(PARI)
A020639(n) = if(1==n, n, vecmin(factor(n)[, 1]));
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Apr 07 2003
EXTENSIONS
Changed "was found" to "exists" in definition. - N. J. A. Sloane, Jan 29 2022
STATUS
approved