Opposite of the digital root!
JavaScript (ES6), 27 31 30 bytes

Returns 0 for 0 or an array of solutions otherwise.

n=&gt;n&amp;&amp;[...1e9+''].map(_=&gt;n+=9)


Demo



let f =

n=&gt;n&amp;&amp;[...1e9+''].map(_=&gt;n+=9)

for(n = 0; n &lt; 10; n++) {
  console.log(n, JSON.stringify(f(n)));
}