A328043 Number of divisors of the amicable pairs.

12, 6, 12, 12, 12, 12, 12, 12, 16, 12, 16, 16, 32, 16, 20, 10, 24, 12, 20, 20, 32, 32, 48, 24, 32, 16, 48, 24, 48, 24, 20, 20, 24, 16, 32, 16, 20, 20, 20, 20, 32, 16, 24, 24, 36, 12, 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

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..20000

Formula

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

Example

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.

Mathematica

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 *)

Crossrefs

Row lengths of A328009.

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

Sequence in context: A084067 A240537 A227354 * A075247 A257841 A173853

Adjacent sequences: A328040 A328041 A328042 * A328044 A328045 A328046

Keyword

nonn

Author

Omar E. Pol, Oct 02 2019

Status

approved