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A199992 Composite numbers whose multiplicative persistence is 2. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified September 24 23:43 EDT 2022. Contains 356951 sequences. (Running on oeis4.)