I can't see a direct pattern, but consider this, a number of string length >2 can be reduced to a single number using modular arithmetic.
In your case consider when
For example as 4 is the remainder of 9 once divided by 5
For longer strings
I can't see a direct pattern, but consider this, a number of string length >2 can be reduced to a single number using modular arithmetic.
In your case consider when
For example as 4 is the remainder of 9 once divided by 5
For longer strings
@Plato, the rule's actually pretty simple (it's not like, take the sum of the digits then multiply by 11 and divide by the product of the digits and take the floor value).
I know the solution as well so it's not that obscure. For example:
8244 --> 4
4567 --> 2
8189 --> 5 (Chook943 can verify these to be correct)