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A082061 Greatest common prime-divisor of n and phi(n)=A000010(n); a(n)=1 if no common prime-divisor was found. 7
1, 1, 1, 2, 1, 2, 1, 2, 3, 2, 1, 2, 1, 2, 1, 2, 1, 3, 1, 2, 3, 2, 1, 2, 5, 2, 3, 2, 1, 2, 1, 2, 1, 2, 1, 3, 1, 2, 3, 2, 1, 3, 1, 2, 3, 2, 1, 2, 7, 5, 1, 2, 1, 3, 5, 2, 3, 2, 1, 2, 1, 2, 3, 2, 1, 2, 1, 2, 1, 2, 1, 3, 1, 2, 5, 2, 1, 3, 1, 2, 3, 2, 1, 3, 1, 2, 1, 2, 1, 3, 1, 2, 3, 2, 1, 2, 1, 7, 3, 5, 1, 2, 1, 2, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

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

FORMULA

a(n) = A006530(A009195(n)). - Antti Karttunen, Nov 03 2017

MAPLE

gcpd := proc(a, b) local g , d ; g := 1 ; for d in numtheory[divisors](a) intersect numtheory[divisors](b) do if isprime(d) then g := max(g, d) ; end if; end do: g ; end proc:

A082061 := proc(n) gcpd( numtheory[phi](n), n) ; end proc: # R. J. Mathar, Jul 09 2011

MATHEMATICA

(* factors/exponent SET *) 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_] := x; f2[x_] := EulerPhi[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@ #} &, 105] (* Michael De Vlieger, Nov 03 2017 *)

PROG

(PARI) gpf(n)=if(n>1, my(f=factor(n)[, 1]); f[#f], 1)

a(n)=gpf(gcd(eulerphi(n), n)) \\ Charles R Greathouse IV, Feb 19 2013

CROSSREFS

Cf. A000010, A006530, A009195.

Cf. also A082062, A082063, A082064, A082065, A082066, A082067.

Sequence in context: A089611 A248470 A082067 * A327979 A107286 A087039

Adjacent sequences:  A082058 A082059 A082060 * A082062 A082063 A082064

KEYWORD

nonn

AUTHOR

Labos Elemer, Apr 07 2003

STATUS

approved

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Last modified February 22 09:15 EST 2020. Contains 332133 sequences. (Running on oeis4.)