A087801 Greatest common divisor of tau(n)+sigma(n) and tau(n)*sigma(n), where tau = A000005 and sigma = A000203.

1, 1, 2, 1, 4, 16, 2, 1, 1, 2, 2, 2, 4, 4, 4, 1, 4, 9, 2, 12, 4, 8, 2, 4, 1, 2, 4, 2, 4, 16, 2, 3, 4, 2, 4, 1, 4, 16, 4, 2, 4, 8, 2, 18, 12, 4, 2, 2, 3, 9, 4, 4, 4, 64, 4, 64, 4, 2, 2, 36, 4, 4, 2, 1, 8, 8, 2, 12, 4, 8, 2, 9, 4, 2, 2, 2, 4, 16, 2, 4, 1, 2, 2, 4, 16, 8, 4, 4, 4, 6, 4, 6, 4, 4, 4, 24

Offset: 1

Author

Reinhard Zumkeller, Oct 11 2003

Keywords

• nonn

Comments

a(n) = GCD(A007503(n), A064840(n)).

Links

• Antti Karttunen, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A009191, A009194, A009205, A007503, A064840, A286360.

Programs

Mathematica

GCD[Total[#],Times@@#]&/@Table[{DivisorSigma[0,n],DivisorSigma[1,n]},{n,100}] (* Harvey P. Dale, Jul 17 2018 *)

PARI

A087801(n) = gcd(sigma(n)+numdiv(n), sigma(n)*numdiv(n)); \\ Antti Karttunen, May 22 2017