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A031346
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Multiplicative persistence: number of iterations of "multiply digits" needed to reach a number < 10.
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51
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0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 1, 1, 1, 2, 2, 2, 2, 3, 2, 3, 1, 1, 2, 2, 2, 3, 2, 3, 2, 3, 1, 1, 2, 2, 2, 2, 3, 2, 3, 3, 1, 1, 2, 2, 3, 3, 2, 4, 3, 3, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 1, 1, 2, 3, 3, 3, 3, 3, 3, 2
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OFFSET
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0,26
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REFERENCES
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M. Gardner, Fractal Music, Hypercards and More Mathematical Recreations from Scientific American, Persistence of Numbers, pp. 120-1; 186-7, W. H. Freeman NY 1992.
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LINKS
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FORMULA
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EXAMPLE
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MAPLE
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MATHEMATICA
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Table[Length[NestWhileList[Times@@IntegerDigits[#]&, n, #>=10&]], {n, 0, 100}]-1 (* Harvey P. Dale, Aug 27 2016 *)
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PROG
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(Python)
from operator import mul
from functools import reduce
mp = 0
while n > 9:
n = reduce(mul, (int(d) for d in str(n)))
mp += 1
return mp
(PARI) a007954(n) = my(d=digits(n)); prod(i=1, #d, d[i])
a(n) = my(k=n, i=0); while(#Str(k) > 1, k=a007954(k); i++); i \\ Felix Fröhlich, Jul 17 2016
(Magma) f:=func<n|&*Intseq(n)>; a:=[]; for n in [0..100] do s:=0; k:=n; while k ge 10 do s:=s+1; k:=f(k); end while; Append(~a, s); end for; a; // Marius A. Burtea, Jan 12 2020
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CROSSREFS
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Cf. A007954 (product of decimal digits of n).
Cf. A010888 (additive digital root of n).
Cf. A031286 (additive persistence of n).
Cf. A031347 (multiplicative digital root of n).
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KEYWORD
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nonn,easy,base
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AUTHOR
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STATUS
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approved
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