Problem #226
Tags:
numeral-system
mathematics
combinatorics
puzzle
c-1
c-0
This task shouldn't be quite difficult, but regard it rather as motivation for research! Thanks to our colleague Kostis K. for suggesting the topic of Multiplicative Persistence as an idea for a problem!
As we have got a bit tired of various tasks about "sum of digits" let's study another integer function, namely "product of digits". It works quite obviously:
PoD(314159) = 3*1*4*1*5*9 = 540
It is evident, that PoD
is always reducing the number, i.e. PoD(x) < x
. (Well, it's not that evident - try to
prove it yourself). And hence consequtive application of PoD
several times should eventually bring us to
single digit value. For example:
3777899 => 666792 => 27216 => 168 => 48 => 32 => 6
How long such chain could be? Surprisingly, that is not known yet! However no one yet found a chain longer
than 11
steps. The length of the chain (number of times PoD
applied) is called
Multiplicative Persistence
for the given number.
Properties of numbers related to their digits are, of course, dependent on the choice of numeral system. For
PoD
function we may expect that larger numeral system base gives less chance of chain halting to 0
. But
moreover it seems that prime bases are much more fruitful.
Let's try to investigate the task in reverse! Given some small value Y
, let's find some larger value X
which comes to that Y
after certain number of PoD
applications. E.g. given 32
as target number,
base 10
for calculations and 5
steps - one of the answers could be 3777899
as in example above.
Or in base 23
, start value F
and 9
steps the answer DEEM
is suitable. Chains of 11
steps could be
found easily in base 23 too - and supposedly longer ones! :)
Input data will give an amount N
of testcases in the first line.
Next lines will give single testcase each, in the form Y B K
where Y
is target, B
base of numeral
system and K
is amount of steps. Of them 10 <= B <= 36
, Y <= B*B
, K <= 7
.
Answer should contain N
source values X
, such that PoD
applied K
times to this X
will yield
corresponding Y
(both Y
and X
written in base B
).
Example
input:
3
A 25 7
34 20 6
28 14 7
answer:
HHHIIN 377BGGIJ 2ACDDDDD