I want to replace plus by comma and the order of numbers in the list should be in increasing order. Example:
a1 + a10 + a11 + a13 + a2 + a27 + a28
In this expression, I want to replace plus sign by comma and delete "a". To get a list of numbers and the order should be
I have tried this, but it's not convenient...
StringReplace["a1 + a 10 + a 11 + a 13 + a2 + a27 + a28" , "+ a" -> ","]