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A225974
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Multiplicative persistence with squares of decimal digits: smallest number such that the number of iterations of "multiply digits squared" needed to reach 0 or 1 equals n.
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2
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OFFSET
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0,2
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COMMENTS
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This sequence is probably finite.
The number of times you need to multiply the square of the digits together before reaching 0 or 1 is equals to n.
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LINKS
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Table of n, a(n) for n=0..6.
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EXAMPLE
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a(4)= 29 -> 4*81 = 324 -> 9*4*16 = 576 -> 25*49*36 = 44100 -> 0 has persistence 4.
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MATHEMATICA
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lst = {}; n = 0; Do[While[True, k = n; c = 0; While[k > 9, k = Times @@ IntegerDigits[k]^2; c++]; If[c == l, Break[]]; n++]; AppendTo[lst, n], {l, 0, 7}]; lst
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CROSSREFS
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Cf. A003001, A031348, A031349.
Sequence in context: A048195 A133634 A174051 * A274046 A014090 A154057
Adjacent sequences: A225971 A225972 A225973 * A225975 A225976 A225977
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KEYWORD
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nonn,hard,fini,base
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AUTHOR
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Michel Lagneau, May 22 2013
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STATUS
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approved
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