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A082065 Greatest common prime-divisor of phi(n)=A000010(n) and sigma(2,n) = A001157(n); a(n) = 1 if no common prime-divisor was found. 7

%I

%S 1,1,2,1,2,2,2,1,1,2,2,2,2,2,2,1,2,1,2,2,2,5,2,2,1,2,2,3,2,2,2,1,5,2,

%T 2,3,2,2,2,2,2,2,2,2,2,2,2,2,3,5,2,3,2,2,2,2,2,2,2,2,2,5,2,1,2,5,2,2,

%U 2,2,2,1,2,2,5,3,5,2,2,2,1,5,2,3,2,2,2,5,2,2,2,2,5,2,2,2,2,3,2,1

%N Greatest common prime-divisor of phi(n)=A000010(n) and sigma(2,n) = A001157(n); a(n) = 1 if no common prime-divisor was found.

%H Michael De Vlieger, <a href="/A082065/b082065.txt">Table of n, a(n) for n = 1..10000</a>

%p 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:

%p A082065 := proc(n) gcpd( numtheory[phi](n), numtheory[sigma][2](n) ) ; end proc:

%p seq(A082065(n),n=1..120) ; # _R. J. Mathar_, Jul 09 2011

%t Table[FactorInteger[GCD[EulerPhi@ n, DivisorSigma[2, n]]][[-1, 1]], {n, 100}] (* _Michael De Vlieger_, Jul 22 2017 *)

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

%o a(n)=gpf(gcd(eulerphi(n),sigma(n,2))) \\ _Charles R Greathouse IV_, Feb 21 2013

%Y Cf. A006530, A001157, A000010, A082061-A082066.

%K nonn

%O 1,3

%A _Labos Elemer_, Apr 07 2003

%E Values corrected by _R. J. Mathar_, Jul 09 2011

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Last modified February 26 09:27 EST 2020. Contains 332277 sequences. (Running on oeis4.)