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A070005
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Arithmetical mean of prime factors of n is an integer and n is neither a prime nor power of a prime.
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4
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15, 21, 33, 35, 39, 42, 45, 51, 55, 57, 63, 65, 69, 75, 77, 78, 84, 85, 87, 91, 93, 95, 99, 105, 110, 111, 114, 115, 117, 119, 123, 126, 129, 133, 135, 141, 143, 145, 147, 153, 155, 156, 159, 161, 168, 170, 171, 175, 177, 183, 185, 186, 187, 189, 195, 201, 203
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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EXAMPLE
| n=33=3.11, mean=(3+11)/2=6
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MATHEMATICA
| ffi[x_] := Flatten[FactorInteger[x]] lf[x_] := Length[FactorInteger[x]] ba[x_] := Table[Part[ffi[x], 2*w-1], {w, 1, lf[x]}] ep[x_] := Table[Part[ffi[x], 2*w], {w, 1, lf[x]}] Do[s=Apply[Plus, ba[n]]/lf[n]; If[IntegerQ[s]&&Greater[lf[n], 1], Print[n]], {n, 2, 1000}]
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CROSSREFS
| Cf. A070006, A001414, A008472.
Sequence in context: A047200 A070537 A184041 * A061346 A046388 A098905
Adjacent sequences: A070002 A070003 A070004 * A070006 A070007 A070008
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KEYWORD
| easy,nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Apr 11 2002
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