RTA (Reverse-Then-Add) root of a number The reverse-then-add (RTA) sequence is a sequence obtained by adding a number to its reverse, and repeating the process on the result. For eg., 

$$ 5 + 5 = 10 \Rightarrow 10 + 01 = 11 \Rightarrow 11 + 11 = 22 \Rightarrow 22 + 22 = 44 \Rightarrow\text{ }...  $$

Thus, 5's RTA sequence contains 10, 11, 22, 44, 88, 176, etc. 

The RTA root of a number \$n\$ is the smallest number that is either equal to \$n\$ or gives raise to \$n\$ in its RTA sequence. 

For eg., 44 is found in the RTA sequence of 5, 10, 11, 13, 22, 31, etc. Of these, 5 is the smallest, and hence RTAroot(44) = 5. 

72 is not part of any number's RTA sequence, and so is considered its own RTA root. 

Input is a positive integer in a range that your language can naturally handle. 

Output is the RTA root of the given number, as defined above. 

Test cases

Input
Output

44
5

72
72

132
3

143
49

1111
1

999
999


Related OEIS: A067031. The output will be a number from this sequence.
Perl 6 Raku, 45 44 39 bytes

{+(1...{$_∈($^a,{$_+.flip}...*&gt;$_)})}

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Explanation:
{                                   }  # Anonymous code block
 +(1...                            )     # Find the first integer
       {                          }      # Where
        $_∈                              # The input is an element of
           (              ...    )         # A sequence defined by
            $^b,                           # The first element is the number we're checking
                {$_+.flip}                 # Each element is the previous element plus its reverse
                             *&gt;$_          # The last element is larger than the input