# Rosetta: Count in factors

alister alister.ware at ntlworld.com
Sun Apr 30 06:47:10 EDT 2017

```On Sat, 29 Apr 2017 22:05:16 +0000, Robert L. wrote:

>>
>> Write a program which counts up from 1, displaying each number as the
>> multiplication of its prime factors.
>>
>> For the purpose of this task, 1 (unity) may be shown as itself.
>>
>>
>> Example
>>
>>    2   is prime,   so it would be shown as itself. 6   is not prime;
>>    it would be shown as   2 x 3
>> 2144   is not prime;   it would be shown as   2 x 2 x 2 x 2 x 2 x 67
>
>
> require 'prime'
>
> puts " 1: 1" ; (2..23).each{|n|
>   printf "%2d: %s\n", n,
>     Prime.prime_division(n).map{|f,c| ([f]*c).join ' x '}.join(' x ')
> }
>
>  1: 1 2: 2 3: 3 4: 2 x 2 5: 5 6: 2 x 3 7: 7 8: 2 x 2 x 2 9: 3 x 3
> 10: 2 x 5 11: 11 12: 2 x 2 x 3 13: 13 14: 2 x 7 15: 3 x 5 16: 2 x 2 x 2
> x 2 17: 17 18: 2 x 3 x 3 19: 19 20: 2 x 2 x 5 21: 3 x 7 22: 2 x 11 23:
> 23

It does not help a student if you do their homework for them,

much better to provide hints & guidance

--
Why do mathematicians insist on using words that already have another
meaning?  "It is the complex case that is easier to deal with."  "If it
doesn't happen at a corner, but at an edge, it nonetheless happens at a
corner."
```