# What is a Well-toned Number™?

This puzzle is based off the What is a Word™ and What is a Phrase™ series started by JLee and their spin-off What is a Number™ series started by smriti.

If a number conforms to a certain rule, I call it a Well-toned Number™. Use the following examples to find the rule:

Here is a CSV version:

Well-toned Numbers™,Not Well-toned Numbers™
36,49
343,729
2000,1000
13597,13579
254708,125678
807452,876521
5551205,5552106
8675190,8675309
138076942564,138076942546
942564138076,942546138076


The puzzle relies on the series' inbuilt assumption, that each number can be tested for whether it is a Well-toned Number™ on its own. In particular, a number's relationship to other numbers in the sequence is irrelevant.

These are not the only examples of Well-toned Numbers™ (or not Well-toned Numbers™), more can be found.

Hints:

• While 8675309 may not be a well-toned number, it is a well-tutoned number! :-D – Darf Nader Feb 1 '18 at 11:53
• Should I phone a friend for the answer? – James Webster Feb 8 '18 at 7:11

Well-toned numbers, when read left to right, have their $n$th digit in the same column as if they were read right to left. The implication is that they resolve the column melody in a symmetric way in terms of DTMF frequencies.