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 A199997 Composite numbers whose multiplicative persistence is 7. 0

%I #9 Aug 03 2014 14:01:36

%S 68889,68898,68988,69888,86889,86898,86988,88689,88698,88869,88896,

%T 88968,88986,89688,89868,89886,96888,98688,98868,98886,168889,168898,

%U 168988,169888,186898,186988,188689,188698,188896,188968,188986,189688,189868,189886,196888

%N Composite numbers whose multiplicative persistence is 7.

%C Complement of A046507 with respect to A046516.

%e 68889 -> [ 27648 ][ 2688 ][ 768 ][ 336 ][ 54 ][ 20 ][ 0 ] -> one digit in seven steps.

%t 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 *)

%Y Cf. A046507 (primes whose multiplicative persistence is 7).

%K nonn,base

%O 1,1

%A _Jaroslav Krizek_, Nov 13 2011

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Last modified May 28 19:55 EDT 2024. Contains 372919 sequences. (Running on oeis4.)