A045766 Number of prime factors of double factorials n!! (A006882), with multiplicity.

0, 1, 1, 3, 2, 5, 3, 8, 5, 10, 6, 13, 7, 15, 9, 19, 10, 22, 11, 25, 13, 27, 14, 31, 16, 33, 19, 36, 20, 39, 21, 44, 23, 46, 25, 50, 26, 52, 28, 56, 29, 59, 30, 62, 33, 64, 34, 69, 36, 72, 38, 75, 39, 79, 41, 83, 43, 85, 44, 89, 45, 91, 48, 97, 50, 100, 51, 103, 53, 106, 54, 111

Offset

1,4

Links

Table of n, a(n) for n=1..72.

Index entries for sequences related to factorial numbers

Example

8!!=8*6*4*2=2^3*2*3*2^2*2=2^7*3. Eight prime factors, so a(8)=8.

Mathematica

PrimeOmega[Range[80]!!] (* Harvey P. Dale, May 29 2015 *)

Crossrefs

Sequence in context: A075889 A181771 A238628 * A281668 A132817 A131025

Adjacent sequences: A045763 A045764 A045765 * A045767 A045768 A045769

Keyword

nonn,easy

Author

Jeff Burch

Status

approved