A328043 - OEIS

%I #40 Oct 17 2019 02:00:48

%S 12,6,12,12,12,12,12,12,16,12,16,16,32,16,20,10,24,12,20,20,32,32,48,

%T 24,32,16,48,24,48,24,20,20,24,16,32,16,20,20,20,20,32,16,24,24,36,12,

%U 24,12,48,16,32,16,20,20,18,36,20,20,48,48,32,16,32,16,32,16,32,16,32,16,48,24,32,16,48,32,24,20

%N Number of divisors of the amicable pairs.

%H Amiram Eldar, <a href="/A328043/b328043.txt">Table of n, a(n) for n = 1..20000</a>

%F a(n) = A000005(A259180(n)).

%e Consider the first amicable pair [220, 284]. The smaller member has 12 divisors, they are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55, 110, 220. The larger member has 6 divisors, they are 1, 2, 4, 71, 142, 284. So a(1) = 12 and a(2) = 6.

%t With[{s = Array[{#, DivisorSigma[1, #] - #} &, 10^5]}, DivisorSigma[0, #] &@ Flatten@ DeleteDuplicates[Sort /@ Select[Reverse /@ s, And[! FreeQ[s, #], UnsameQ @@ #] &]]] (* _Michael De Vlieger_, Oct 08 2019 *)

%Y Row lengths of A328009.

%Y Cf. A000005, A259180, A328063, A328064, A328065.

%K nonn

%O 1,1

%A _Omar E. Pol_, Oct 02 2019