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

1,3

LINKS

Michael De Vlieger, Table of n, a(n) for n = 1..10000

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:

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

seq(A082065(n), n=1..120) ; # R. J. Mathar, Jul 09 2011

MATHEMATICA

Table[FactorInteger[GCD[EulerPhi@ n, DivisorSigma[2, n]]][[-1, 1]], {n, 100}] (* Michael De Vlieger, Jul 22 2017 *)

PROG

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

a(n)=gpf(gcd(eulerphi(n), sigma(n, 2))) \\ Charles R Greathouse IV, Feb 21 2013

CROSSREFS

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

Sequence in context: A304943 A248597 A082071 * A082070 A082902 A123926

Adjacent sequences:  A082062 A082063 A082064 * A082066 A082067 A082068

KEYWORD

nonn

AUTHOR

Labos Elemer, Apr 07 2003

EXTENSIONS

Values corrected by R. J. Mathar, Jul 09 2011

STATUS

approved

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Last modified January 17 12:42 EST 2020. Contains 330958 sequences. (Running on oeis4.)