A366898 Number of divisors of n*2^n - 1, the Woodall (or Riesel) numbers.

1, 2, 2, 6, 4, 2, 4, 4, 4, 4, 6, 4, 12, 10, 8, 48, 8, 4, 8, 4, 16, 16, 8, 8, 4, 8, 8, 16, 24, 2, 8, 4, 8, 32, 8, 32, 4, 8, 4, 24, 16, 8, 32, 8, 16, 24, 40, 16, 16, 8, 8, 16, 24, 8, 16, 8, 16, 6, 32, 8, 8, 16, 8, 512, 48, 16, 12, 48, 16, 8, 8, 4, 24, 16, 2, 256

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..865

Formula

a(n) = sigma0(n*2^n - 1) = A000005(A003261(n)).

Mathematica

Table[DivisorSigma[0, n*2^n - 1], {n, 1, 100}] (* Amiram Eldar, Dec 11 2023 *)

Prog

(PARI) a(n) = numdiv(n*2^n - 1); \\ Amiram Eldar, Dec 11 2023

Crossrefs

Cf. A000005, A003261, A002234, A242273, A063515, A056821, A367006, A366899.

Sequence in context: A324349 A092384 A061915 * A138565 A137316 A064851

Adjacent sequences: A366895 A366896 A366897 * A366899 A366900 A366901

Keyword

nonn

Author

Tyler Busby, Oct 26 2023

Status

approved