-that is, the question as to whether corresponding statements are also valid for all two-digit numbers. (It is noteworthy that in the two-digit numbers the number-mirror number difference and the difference from the minimum and maximum numbers are identical.) More interesting and more complicated-are analogous the orems also valid for four-digit numbers? For four-digit numbers we find that the differences, maximum numbers minus minimum numbers," in nearly all cases end after no more than seven steps with the number 6174. (See"An Arithmetical Curiosity, Arithmetic Teacher, April 1979 pp. 23-24.)