OFFSET
1,6
COMMENTS
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Will Nicholes, Prime Signatures
EXAMPLE
72 (2^3*3^2) has 2 distinct prime factors. Since 72 = A181800(8), a(8) = 2.
CROSSREFS
KEYWORD
nonn
AUTHOR
Matthew Vandermast, Jun 04 2012
STATUS
approved