A366899 Number of prime factors of n*2^n - 1, counted with multiplicity.

0, 1, 1, 3, 2, 1, 2, 2, 2, 2, 3, 2, 4, 5, 4, 6, 3, 2, 3, 2, 4, 5, 3, 3, 2, 3, 3, 4, 5, 1, 3, 2, 3, 5, 3, 5, 2, 3, 2, 5, 4, 3, 5, 3, 4, 5, 7, 4, 4, 3, 3, 4, 5, 3, 4, 3, 4, 3, 5, 3, 3, 4, 3, 9, 6, 4, 4, 6, 4, 3, 3, 2, 5, 4, 1, 9, 3, 4, 5, 2, 1, 4, 5, 6, 2, 3, 4

Offset

1,4

Comments

The numbers n*2^n-1 are called Woodall (or Riesel) numbers.

Links

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

Formula

a(n) = bigomega(n*2^n - 1) = A001222(A003261(n)).

Mathematica

Table[PrimeOmega[n*2^n - 1], {n, 1, 100}] (* Amiram Eldar, Dec 09 2023 *)

Prog

(PARI) a(n) = bigomega(n*2^n - 1); \\ Michel Marcus, Dec 09 2023

Crossrefs

Cf. A001222, A003261, A085723, A366898 (divisors), A367006 (without multiplicity).

Sequence in context: A079099 A213195 A256794 * A068929 A060567 A174543

Adjacent sequences: A366896 A366897 A366898 * A366900 A366901 A366902

Keyword

nonn

Author

Tyler Busby, Oct 26 2023

Status

approved