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A351563
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a(n) is the exponent of the second smallest prime factor of n, or 0 if n is a power of a prime.
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2
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0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 0, 2, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 1, 1, 1, 2, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 2, 1, 1, 0, 3, 1, 1, 1, 1, 0, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 2, 0, 1, 2, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 2, 1, 1, 1, 1, 1, 1, 0, 2, 1, 2, 0, 1, 0, 1, 1, 1, 0, 3
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OFFSET
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1,18
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LINKS
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FORMULA
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EXAMPLE
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For n = 4 = 2^2 there is no second smallest prime factor as 4 is a power of prime, therefore a(4) = 0.
For n = 18 = 2^1 * 3^2, the exponent of the second smallest prime factor (3) is 2, therefore a(18) = 2.
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MATHEMATICA
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Array[If[Length[#] < 2, 0, #[[2, -1]]] &@ FactorInteger[#] &, 108] (* Michael De Vlieger, Apr 01 2022 *)
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PROG
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(PARI) A351563(n) = if(1>=omega(n), 0, (factor(n))[2, 2]);
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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