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A112753
Number of distinct prime factors of n-th number of the form 3^i*5^j.
4
0, 1, 1, 1, 2, 1, 1, 2, 2, 1, 1, 2, 2, 1, 2, 2, 1, 2, 1, 2, 2, 2, 2, 1, 1, 2, 2, 2, 2, 1, 2, 2, 2, 1, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 1, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 2, 2
OFFSET
1,5
LINKS
FORMULA
a(n) = A001221(A003593(n)) = 2 - 0^A022336(n) + 0^A022337(n);
a(n) <= 2.
MATHEMATICA
With[{nn=120}, Take[PrimeNu/@Union[Flatten[{3^#[[1]] 5^#[[2]], 5^#[[1]] 3^#[[2]]}&/@Tuples[Range[0, nn], 2]]], nn]] (* Harvey P. Dale, Nov 29 2013 *)
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Sep 18 2005
STATUS
approved