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A104484
Number of distinct prime divisors of 33...331 (with n 3s).
7
0, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 3, 3, 4, 2, 2, 3, 1, 3, 4, 3, 2, 4, 3, 3, 2, 4, 3, 3, 2, 3, 4, 6, 2, 2, 3, 3, 4, 4, 1, 3, 3, 6, 6, 3, 2, 3, 5, 3, 1, 3, 3, 4, 6, 3, 3, 5, 3, 5, 1, 3, 6, 5, 4, 3, 5, 3, 3, 5, 4, 6, 6, 3, 6, 2, 2, 4, 1, 5, 5, 5, 4, 4, 7, 2, 2, 5, 6
OFFSET
0,9
COMMENTS
Interestingly, the first seven members in this sequence are all primes.
LINKS
FORMULA
a(n) = A001221(A033175(n+1)). - Amiram Eldar, Jan 24 2020, corrected, May 13 2020
EXAMPLE
Number of distinct prime divisors of 31 is 1 (prime).
Number of distinct prime divisors of 331 is 1 (prime).
Number of distinct prime divisors of 3331 is 1 (prime).
Number of distinct prime divisors of 33331 is 1 (prime).
Number of distinct prime divisors of 333331 is 1 (prime).
Number of distinct prime divisors of 3333331 is 1 (prime).
Number of distinct prime divisors of 33333331 is 1 (prime).
MATHEMATICA
Table[Length[FactorInteger[(10^(n + 1) - 7)/3]], {n, 1, 50}] (* Stefan Steinerberger *)
PROG
(PARI) a(n) = omega((10^(n + 1) - 7)/3); \\ Michel Marcus, May 13 2020
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Parthasarathy Nambi, Apr 18 2005
EXTENSIONS
More terms from Amiram Eldar, Jan 24 2020
a(0) inserted by Amiram Eldar, May 13 2020
STATUS
approved