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A284149
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a(n) = smallest number whose arithmetic derivative has exactly n prime factors.
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0
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6, 4, 8, 12, 16, 92, 64, 144, 508, 256, 1024, 3392, 8192, 3072, 13248, 19456, 114688, 81920, 65536, 262144, 671744, 1048576, 983040, 1835008, 5296128, 9437184, 16777216, 54525952, 121634816, 201326592, 587202560, 738197504, 3340500992, 6710886400, 3959422976, 4294967296, 28991029248, 18253611008, 68719476736
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OFFSET
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1,1
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LINKS
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EXAMPLE
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a(1) = 6 because 6' = 5;
a(2) = 4 because 4' = 4 = 2 * 2;
a(3) = 8 because 8' = 12 = 2 * 2 * 3.
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MAPLE
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with(numtheory): P:= proc(q) local k, n; for n from 1 to q do for k from 1 to q do
if bigomega(k*add(op(2, p)/op(1, p), p=ifactors(k)[2]))=n then print(k); break; fi;
od; od; end: P(10^9);
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MATHEMATICA
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ad[1]=0; ad[n_] := n*Total[ (#1[[2]] / #1[[1]] &) /@ FactorInteger[n]]; a[n_] := Block[{k=2}, While[PrimeOmega@ ad[k] != n, k++]; k]; Array[a, 15] (* Giovanni Resta, Mar 22 2017 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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