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A199997
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Composite numbers whose multiplicative persistence is 7.
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0
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68889, 68898, 68988, 69888, 86889, 86898, 86988, 88689, 88698, 88869, 88896, 88968, 88986, 89688, 89868, 89886, 96888, 98688, 98868, 98886, 168889, 168898, 168988, 169888, 186898, 186988, 188689, 188698, 188896, 188968, 188986, 189688, 189868, 189886, 196888
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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68889 -> [ 27648 ][ 2688 ][ 768 ][ 336 ][ 54 ][ 20 ][ 0 ] -> one digit in seven steps.
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MATHEMATICA
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persistence[n_] := Module[{cnt = 0, k = n}, While[k > 9, cnt++; k = Times @@ IntegerDigits[k]]; cnt]; Select[Range[300000], ! PrimeQ[#] && persistence[#] == 7 &] (* T. D. Noe, Nov 23 2011 *)
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CROSSREFS
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Cf. A046507 (primes whose multiplicative persistence is 7).
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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