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

1,1

Comments

Complement of A046502 with respect to A046511.

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

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

Sequence in context: A133507 A046511 A140058 * A242221 A186538 A340271

Adjacent sequences: A199989 A199990 A199991 * A199993 A199994 A199995

Keyword

nonn,base

Author

Jaroslav Krizek, Nov 13 2011

Status

approved