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A104524
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Number of distinct prime divisors of 55...557 (with n 5s).
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3
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2, 1, 1, 2, 1, 3, 3, 3, 1, 3, 2, 5, 3, 1, 4, 3, 3, 3, 4, 2, 1, 2, 7, 4, 4, 4, 4, 5, 4, 4, 3, 2, 3, 5, 3, 4, 3, 7, 2, 4, 2, 4, 4, 8, 2, 4, 3, 6, 3, 2, 4, 7, 7, 7, 5, 5, 6, 7, 2, 4, 6, 3, 5, 5, 2, 5, 2, 4, 5, 5, 3, 9, 10, 6, 5, 6, 4, 4, 4, 5, 4, 5, 3, 6, 6, 4, 1
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OFFSET
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1,1
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LINKS
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FORMULA
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EXAMPLE
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The number of distinct prime divisors of 57 is 2.
The number of distinct prime divisors of 557 is 1 (prime).
The number of distinct prime divisors of 5557 is 1 (prime).
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MAPLE
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A104524 := proc(n) local x ; x := [7, seq(5, 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
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MATHEMATICA
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Table[PrimeNu[(50*10^n + 13)/9], {n, 1, 50}](* G. C. Greubel, May 07 2017 *)
Table[PrimeNu[FromDigits[PadLeft[{7}, n, 5]]], {n, 2, 90}] (* Harvey P. Dale, Dec 03 2021 *)
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PROG
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(PARI) a(n) = omega((5*10^(n+1)+13)/9); \\ Michel Marcus, May 08 2017
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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