OFFSET
1,2
COMMENTS
Also number of distinct prime factors of (10^(n + 1) - 1)*7/9 - 6. - Stefan Steinerberger, Mar 01 2006
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..231
FORMULA
EXAMPLE
The number of distinct prime divisors of 71 is 1 (prime).
The number of distinct prime divisors of 771 is 2.
The number of distinct prime divisors of 7771 is 2.
MATHEMATICA
Table[Length[FactorInteger[(10^(n + 1) - 1)*7/9 - 6]], {n, 1, 50}] (* Stefan Steinerberger, Mar 01 2006 *)
PrimeNu/@(FromDigits/@Table[PadLeft[{1}, n, 7], {n, 2, 55}]) (* Harvey P. Dale, Apr 22 2011 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Parthasarathy Nambi, Apr 20 2005
EXTENSIONS
More terms from Stefan Steinerberger, Mar 01 2006
Offset corrected and more terms added by Amiram Eldar, Jan 24 2020
STATUS
approved