A057957 - OEIS

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A057957

Number of prime factors of 4^n - 1 (counted with multiplicity).

19

1, 2, 3, 3, 3, 5, 3, 4, 6, 6, 4, 7, 3, 6, 7, 5, 3, 10, 3, 8, 8, 7, 4, 10, 7, 7, 9, 8, 6, 13, 3, 7, 9, 7, 9, 14, 5, 7, 8, 10, 5, 14, 5, 10, 13, 9, 6, 13, 5, 14, 11, 10, 6, 15, 12, 11, 9, 9, 6, 17, 3, 8, 14, 9, 9, 15, 5, 11, 9, 16, 6, 19, 6, 10, 14, 11, 10, 18, 5, 13, 16, 10, 8, 19, 7, 10, 11

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Max Alekseyev, Table of n, a(n) for n = 1..1122 (first 603 terms from Amiram Eldar)

S. S. Wagstaff, Jr., The Cunningham Project

FORMULA

Mobius transform of A085029. - T. D. Noe, Jun 19 2003

a(n) = A001222(A024036(n)) = A046051(2*n). - Amiram Eldar, Feb 01 2020

MATHEMATICA

PrimeOmega/@(4^Range[90]-1) (* Harvey P. Dale, Dec 31 2018 *)

CROSSREFS

bigomega(b^n-1): A057951 (b=10), A057952 (b=9), A057953 (b=8), A057954 (b=7), A057955 (b=6), A057956 (b=5), this sequence (b=4), A057958 (b=3), A046051 (b=2).

Cf. A001222, A024036, A054992, A085029, A274906.

Sequence in context: A020481 A066660 A361687 * A359507 A366660 A241686

Adjacent sequences: A057954 A057955 A057956 * A057958 A057959 A057960

KEYWORD

nonn

AUTHOR

Patrick De Geest, Nov 15 2000

STATUS

approved