The aim of this paper is to show that for any n ¥ N, n > 3, there exist a, b ¥ N*
such that n=a+b, the ‘‘lengths’’ of a and b having the same parity (see the text for
the definition of the ‘‘length’’ of a natural number). Also we will show that for any
n ¥ N, n > 2, n ] 5, 10, there exist a, b ¥ N* such that n=a+b, the ‘‘lengths’’ of a
and b having different parities. We will prove also that for any prime p — 7(mod 8)
there exist a, b ¥ N* such that p=a2
+b, the ‘‘length’’ of b being an even number.