has an infinite number of solutions, of which one is (-1 , 1, 1). (The common difference, d, is the same in the three distinct arithmetic sequences.) The proof is very similar to that given just above in the special case when n= a + 4d and q = a+ 8d. Thus, Nicolai’s case is a special case of the general situation where n and q are numbers of an arithmetic sequence having a as the first term.