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A082064 Greatest common prime-divisor of phi(n) and sigma(n) = A000203(n); a(n)=1 if no common prime-divisor was found. 4
1, 1, 2, 1, 2, 2, 2, 1, 1, 2, 2, 2, 2, 3, 2, 1, 2, 3, 2, 2, 2, 2, 2, 2, 1, 3, 2, 2, 2, 2, 2, 1, 2, 2, 3, 1, 2, 3, 2, 2, 2, 3, 2, 2, 3, 2, 2, 2, 3, 1, 2, 2, 2, 3, 2, 3, 2, 2, 2, 2, 2, 3, 2, 1, 3, 2, 2, 2, 2, 3, 2, 3, 2, 3, 2, 2, 3, 3, 2, 2, 1, 2, 2, 2, 2, 3, 2, 5, 2, 3, 2, 2, 2, 2, 3, 2, 2, 3, 3, 1, 2, 2, 2, 3, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..16384

FORMULA

a(n) = A006530(A009223(n)). - Antti Karttunen, Nov 03 2017

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_] := EulerPhi[n]; f2[x_] := DivisorSigma[1, x]; Table[Max[Intersection[ba[f1[w]], ba[f2[w]]]], {w, 1, 128}]

(* Second program: *)

Array[If[CoprimeQ[#1, #2], 1, Max@ Apply[Intersection, Map[FactorInteger[#][[All, 1]] &, {#1, #2}]]] & @@ {EulerPhi@ #, DivisorSigma[1, #]} &, 105] (* Michael De Vlieger, Nov 03 2017 *)

PROG

(PARI)

A006530(n) = if(1==n, n, vecmax(factor(n)[, 1]));

A082064(n) = A006530(gcd(eulerphi(n), sigma(n))); \\ Antti Karttunen, Nov 03 2017

CROSSREFS

Cf. A000010, A000203, A006530, A009223.

Cf. also A082061, A082062, A082063, A082065, A082066, A082070.

Sequence in context: A082070 A082902 A123926 * A082055 A073812 A009223

Adjacent sequences:  A082061 A082062 A082063 * A082065 A082066 A082067

KEYWORD

nonn

AUTHOR

Labos Elemer, Apr 07 2003

STATUS

approved

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Last modified April 6 10:53 EDT 2020. Contains 333273 sequences. (Running on oeis4.)