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A231817
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Multiplicative digital root of concatenation of all divisors of n (A037278).
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1
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1, 2, 3, 8, 5, 8, 7, 8, 4, 0, 1, 6, 3, 0, 5, 0, 7, 0, 9, 0, 8, 8, 6, 8, 0, 4, 6, 0, 8, 0, 3, 0, 4, 6, 0, 0, 2, 8, 8, 0, 4, 0, 2, 0, 0, 6, 6, 0, 0, 0, 0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 6, 4, 0, 0, 0, 0, 8, 0, 2, 0, 7, 0, 2, 8, 0, 0, 8, 0, 8, 0, 0, 6, 8, 0, 0, 0, 0
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OFFSET
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1,2
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COMMENTS
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Also multiplicative digital root of A190997 (product of digits of all the divisors of n) or A007955 (product of divisors of n).
Conjecture: a(n) = 0 for almost all n.
793 of the first 1000 terms are zeros, and 9147 out of the first 10000 terms are zeros. - Harvey P. Dale, Jul 30 2019
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LINKS
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EXAMPLE
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For n=12: 1*2*3*4*6*1*2=288, 2*8*8=128, 1*2*8=16, 1*6=6; a(12)=6.
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MATHEMATICA
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Table[NestWhile[Times@@IntegerDigits[#]&, Times@@Flatten[ IntegerDigits/@ Divisors[ n]], #>9&], {n, 90}] (* Harvey P. Dale, Jul 30 2019 *)
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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