OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
125 -> 1 * 2 * 5-> [ 10 ] -> 1 * 0 -> [ 0 ] -> one digit in two steps.
MATHEMATICA
persistence[n_] := Module[{cnt = 0, k = n}, While[k > 9, cnt++; k = Times @@ IntegerDigits[k]]; cnt]; Select[Range[400], ! PrimeQ[#] && persistence[#] == 2 &] (* T. D. Noe, Nov 23 2011 *)
Select[Range[250], CompositeQ[#]&&Length[NestWhileList[Times@@ IntegerDigits[ #]&, #, #>9&]] == 3&] (* Harvey P. Dale, Apr 10 2015 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Jaroslav Krizek, Nov 13 2011
STATUS
approved