231437domain: NAppears in sequencesSum{T(n-k,k)}, 0<=k<=[ n/2 ], T given by A026681.at n=23A026691Composite 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.at n=31A239724