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A105259
Number of distinct prime divisors of 99..91 (with n 9's).
2
0, 2, 1, 2, 1, 3, 1, 4, 2, 3, 3, 3, 3, 4, 3, 4, 3, 6, 2, 4, 4, 3, 3, 5, 4, 7, 4, 6, 2, 6, 3, 6, 1, 2, 3, 5, 3, 10, 4, 7, 5, 4, 6, 7, 1, 7, 2, 6, 3, 5, 5, 6, 4, 6, 2, 8, 4, 7, 3, 5, 4, 11, 2, 7, 5, 8, 6, 5, 5, 7, 2, 8, 4, 7, 5, 6, 4, 6, 5, 9, 3, 9, 4, 7, 2, 9, 4
OFFSET
0,2
LINKS
FORMULA
a(n) = A001221(A170955(n+1)). - R. J. Mathar, Aug 24 2011
EXAMPLE
If n=1, then the number of distinct prime divisors of 91 is 2.
If n=2, then the number of distinct prime divisors of 991 is 1 (a prime).
If n=3, then the number of distinct prime divisors of 9991 is 2.
MAPLE
A105259 := proc(n) local x ; x := [1, seq(9, k=1..n)] ; add(op(i, x)*10^(i-1), i=1..nops(x)) ; numtheory[factorset](%) ; nops(%) ; end proc: # R. J. Mathar, Aug 24 2011
MATHEMATICA
Table[PrimeNu[10^(n + 1) - 9], {n, 0, 50}] (* G. C. Greubel, May 10 2017 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Parthasarathy Nambi, Apr 14 2005
EXTENSIONS
More terms from Amiram Eldar, Jan 24 2020
STATUS
approved