Composite numbers k such that if k = a U b (where U denotes concatenation) then a' + b' = k', where a', b' and k' are the arithmetic derivatives of a, b and k.

A239724

Composite numbers k such that if k = a U b (where U denotes concatenation) then a' + b' = k', where a', b' and k' are the arithmetic derivatives of a, b and k.