A199992 Composite numbers whose multiplicative persistence is 2.

25, 26, 27, 28, 34, 35, 36, 38, 44, 45, 46, 48, 52, 54, 56, 58, 62, 63, 64, 65, 72, 76, 82, 84, 85, 92, 99, 125, 126, 128, 129, 134, 135, 136, 138, 143, 144, 145, 146, 148, 152, 153, 154, 156, 158, 162, 164, 165, 172, 176, 182, 183, 184, 185, 192, 215, 216

Offset: 1

Author

Jaroslav Krizek, Nov 13 2011

Keywords

• nonn
• base

Comments

Complement of A046502 with respect to A046511.

Examples

			125 -> 1 * 2 * 5-> [ 10 ] -> 1 * 0 -> [ 0 ] -> one digit in two steps.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A046502 (primes whose multiplicative persistence is 2).

Programs

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 *)