A087801 - OEIS

%I #12 Jul 17 2018 18:08:11

%S 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,

%T 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,

%U 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

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

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

%H Antti Karttunen, <a href="/A087801/b087801.txt">Table of n, a(n) for n = 1..10000</a>

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

%o (PARI) A087801(n) = gcd(sigma(n)+numdiv(n), sigma(n)*numdiv(n)); \\ _Antti Karttunen_, May 22 2017

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

%K nonn

%O 1,3

%A _Reinhard Zumkeller_, Oct 11 2003