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A068999
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Numbers n such that n = (sum of distinct prime factors of n)(product of distinct prime factors of n).
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0
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4, 9, 25, 49, 121, 169, 289, 300, 361, 504, 529, 841, 961, 980, 1056, 1369, 1404, 1575, 1681, 1849, 2209, 2600, 2736, 2809, 3481, 3721, 4489, 4851, 5041, 5329, 6241, 6375, 6696, 6889, 7436, 7448, 7695, 7921, 9409, 9639, 10201, 10304, 10609, 11375, 11449
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Contains all squares of primes (A001248).
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EXAMPLE
| The prime factors of 300 are 2,3,5, the sum and product of which are 10,30 respectively, which multiply to 300. Hence 300 belongs to the sequence.
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MATHEMATICA
| h[n_] := Module[{a, l }, a = FactorInteger[n]; l = Length[a]; Sum[a[[i]][[1]], {i, 1, l}]*Product[a[[i]][[1] ], {i, 1, l}] == n]; Select[Range[2, 10^4], h[ # ] &]
pf[n_] := First /@ FactorInteger[n]; Select[Range[11500], (Plus @@ pf[ # ])*(Times @@ pf[ # ]) == # &] (*Chandler*)
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CROSSREFS
| Sequence in context: A158144 A158145 A082180 * A179707 A077438 A001248
Adjacent sequences: A068996 A068997 A068998 * A069000 A069001 A069002
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KEYWORD
| nonn
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AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Mar 20 2002
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EXTENSIONS
| Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Nov 14 2005
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