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A367006
Number of distinct prime factors of n*2^n - 1.
4
0, 1, 1, 2, 2, 1, 2, 2, 2, 2, 2, 2, 3, 2, 2, 5, 3, 2, 3, 2, 4, 3, 3, 3, 2, 3, 3, 4, 4, 1, 3, 2, 3, 5, 3, 5, 2, 3, 2, 4, 4, 3, 5, 3, 4, 4, 4, 4, 4, 3, 3, 4, 4, 3, 4, 3, 4, 2, 5, 3, 3, 4, 3, 9, 5, 4, 3, 5, 4, 3, 3, 2, 4, 4, 1, 7, 3, 4, 5, 2, 1, 4, 4, 6, 2, 2, 4
OFFSET
1,4
COMMENTS
The numbers n*2^n-1 are called Woodall (or Riesel) numbers.
LINKS
FORMULA
a(n) = omega(n*2^n - 1) = A001221(A003261(n)).
MATHEMATICA
Table[PrimeNu[n*2^n - 1], {n, 1, 100}] (* Amiram Eldar, Dec 11 2023 *)
PROG
(PARI) a(n) = omega(n*2^n - 1); \\ Amiram Eldar, Dec 11 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Sean A. Irvine, Oct 31 2023
STATUS
approved