OFFSET
1,1
EXAMPLE
77 -> [ 49 ][ 36 ][ 18 ][ 8 ] -> one digit in four steps.
MATHEMATICA
persistence[n_] := Module[{cnt = 0, k = n}, While[k > 9, cnt++; k = Times @@ IntegerDigits[k]]; cnt]; Select[Range[1000], ! PrimeQ[#] && persistence[#] == 4 &]
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Jaroslav Krizek, Nov 13 2011
STATUS
approved