cp's OEIS Frontend

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

%I A087801 #12 Jul 17 2018 18:08:11
%S A087801 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 A087801 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 A087801 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 A087801 Greatest common divisor of tau(n)+sigma(n) and tau(n)*sigma(n), where tau = A000005 and sigma = A000203.
%C A087801 a(n) = GCD(A007503(n), A064840(n)).
%H A087801 Antti Karttunen, <a href="/A087801/b087801.txt">Table of n, a(n) for n = 1..10000</a>
%t A087801 GCD[Total[#],Times@@#]&/@Table[{DivisorSigma[0,n],DivisorSigma[1,n]},{n,100}] (* _Harvey P. Dale_, Jul 17 2018 *)
%o A087801 (PARI) A087801(n) = gcd(sigma(n)+numdiv(n), sigma(n)*numdiv(n)); \\ _Antti Karttunen_, May 22 2017
%Y A087801 Cf. A009191, A009194, A009205, A007503, A064840, A286360.
%K A087801 nonn
%O A087801 1,3
%A A087801 _Reinhard Zumkeller_, Oct 11 2003