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A317102
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Powerful numbers whose distinct prime multiplicities are pairwise indivisible.
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8
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1, 4, 8, 9, 16, 25, 27, 32, 36, 49, 64, 72, 81, 100, 108, 121, 125, 128, 169, 196, 200, 216, 225, 243, 256, 288, 289, 343, 361, 392, 432, 441, 484, 500, 512, 529, 625, 648, 675, 676, 729, 800, 841, 864, 900, 961, 968, 972, 1000, 1024, 1089, 1125, 1152, 1156, 1225
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OFFSET
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1,2
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COMMENTS
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A number is powerful if its prime multiplicities are all greater than 1.
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LINKS
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EXAMPLE
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144 = 2^4 * 3^2 is not in the sequence because 4 and 2 are not pairwise indivisible.
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MAPLE
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filter:= proc(n) local L, i, j, q;
L:= convert(map(t -> t[2], ifactors(n)[2]), set);
if min(L) = 1 then return false fi;
for j from 2 to nops(L) do
for i from 1 to j-1 do
q:= L[i]/L[j];
if q::integer or (1/q)::integer then return false fi;
od od;
true
end proc:
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MATHEMATICA
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Select[Range[1000], And[Max@@Last/@FactorInteger[#]>=2, Select[Tuples[Last/@FactorInteger[#], 2], And[UnsameQ@@#, Divisible@@#]&]=={}]&]
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CROSSREFS
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Cf. A001694, A056239, A112798, A118914, A124010, A285572, A285573, A303362, A304713, A316475, A317101, A317616.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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Definition corrected and a(1)=1 inserted by Robert Israel, Jun 23 2019
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STATUS
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approved
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