7 is to 34 as 5 is to

This question is mostly asked as a multiple choice question as we can have different solutions if options are not given.
The most logical way of 34 is to 7 is simple taking the sum of the digits of 34 i.e
3+4=7
5 is to 32,41,50,23,14 etc...all these numbers have sum of the digits as 5.