A104361 Number of divisors of A104357(n) = A104350(n) - 1.

1, 2, 2, 2, 2, 2, 4, 2, 2, 2, 4, 4, 4, 4, 2, 4, 8, 8, 2, 8, 8, 8, 2, 4, 16, 16, 4, 4, 32, 16, 4, 8, 4, 8, 2, 8, 16, 8, 32, 8, 16, 16, 32, 2, 8, 16, 4, 4, 4, 8, 2, 4, 8, 4, 8, 2, 16, 2, 8, 16, 64, 16, 16, 4, 64, 2, 32, 16, 16, 2, 4, 32, 128, 16, 32, 8, 16, 16, 32, 16, 32, 4, 16, 16, 32, 8, 8, 8, 4, 32, 4, 32, 16, 128, 4, 32, 8, 4

Offset: 2

Author

Reinhard Zumkeller, Mar 06 2005

Keywords

• nonn

Links

• Max Alekseyev, Table of n, a(n) for n = 2..145
• Reinhard Zumkeller, Products of largest prime factors of numbers <= n

Crossrefs

Cf. A000005, A064145, A104350, A104357, A104358, A104359, A104360, A104362, A104363, A104364, A104369.

Programs

Mathematica

a[n_] := DivisorSigma[0, -1 + Product[FactorInteger[k][[-1, 1]], {k, 1, n}]]; Array[a, 50, 2] (* Amiram Eldar, Feb 12 2020 *)

Formula

a(n) = A000005(A104357(n)).

Extensions

a(51)-a(74) from Amiram Eldar, Feb 12 2020

Terms a(75) onward from Max Alekseyev, Oct 03 2022