A073806 Number of divisors of sum of square of divisors.

1, 2, 4, 4, 4, 6, 6, 4, 4, 8, 4, 16, 8, 8, 12, 4, 8, 8, 4, 16, 12, 8, 8, 12, 8, 12, 12, 24, 4, 18, 8, 16, 12, 12, 18, 12, 8, 8, 18, 16, 6, 15, 12, 16, 12, 12, 16, 16, 8, 16, 18, 32, 8, 18, 12, 16, 12, 8, 4, 48, 4, 16, 24, 4, 24, 18, 8, 32, 18, 24, 4, 16, 16, 12, 32, 16, 18, 24, 4, 16, 6

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Formula

a(n) = A000005(A001157(n)) = d(sigma(2, n)).

Example

n = 10: D = {1,2,5,10}, sigma(2,10) = 1 + 4 + 25 + 100 = 130, D(130) = {1,2,5,10,13,26,65,130}, so a(10) = 8.

Mathematica

a[n_] := DivisorSigma[0, DivisorSigma[2, n]]; Array[a, 81] (* Amiram Eldar, Aug 01 2019 *)

Crossrefs

Cf. A000005, A000203, A001157, A062068, A073802-A073813.

Sequence in context: A084291 A258573 A060271 * A060849 A130819 A307097

Adjacent sequences: A073803 A073804 A073805 * A073807 A073808 A073809

Keyword

nonn

Author

Labos Elemer, Aug 13 2002

Status

approved