OFFSET
1,4
COMMENTS
Also number of distinct prime factors of 6/9*(10^(n + 1) - 1) - 5. - Stefan Steinerberger, Feb 26 2006
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..199
FORMULA
EXAMPLE
Number of distinct prime divisors of 61 is 1 (prime).
Number of distinct prime divisors of 661 is 1 (prime).
Number of distinct prime divisors of 6661 is 1 (prime).
MATHEMATICA
Table[Length[FactorInteger[6/9*(10^(n + 1) - 1) - 5]], {n, 1, 50}] (* Stefan Steinerberger, Feb 26 2006 *)
Table[PrimeNu[FromDigits[PadLeft[{1}, n, 6]]], {n, 2, 90}] (* Harvey P. Dale, Jun 06 2021 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Parthasarathy Nambi, Apr 24 2005
EXTENSIONS
More terms from Stefan Steinerberger, Feb 26 2006
Offset corrected and more terms added by Amiram Eldar, Jan 24 2020
STATUS
approved