OFFSET
1,2
COMMENTS
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
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
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.
MATHEMATICA
Table[NestWhile[Times@@IntegerDigits[#]&, Times@@Flatten[ IntegerDigits/@ Divisors[ n]], #>9&], {n, 90}] (* Harvey P. Dale, Jul 30 2019 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Jaroslav Krizek, Nov 13 2013
STATUS
approved