MAGIC SQUARES OF PRIMES.

The problem of constructing magic squares with prime numbers only was first discussed by myself in The Weekly Dispatch for 22nd July and 5th August 1900; but during the last three or four years it has received great attention from American mathematicians.  First, they have sought to form these squares with the lowest possible constants.  Thus, the first nine prime numbers, 1 to 23 inclusive, sum to 99, which (being divisible by 3) is theoretically a suitable series; yet it has been demonstrated that the lowest possible constant is 111, and the required series as follows:  1, 7, 13, 31, 37, 43, 61, 67, and 73.  Similarly, in the case of the fourth order, the lowest series of primes that are “theoretically suitable” will not serve.  But in every other order, up to the 12th inclusive, magic squares have been constructed with the lowest series of primes theoretically possible.  And the 12th is the lowest order in which a straight series of prime numbers, unbroken, from 1 upwards has been made to work.  In other words, the first 144 odd prime numbers have actually been arranged in magic form.  The following summary is taken from The Monist (Chicago) for October 1913:—­

Order of Totals of Lowest Squares
Square.  Series.  Constants. made by—­
(Henry E.
3rd 333 111 { Dudeney
( (1900).

(Ernest Bergholt
4th 408 102 { and C. D.
( Shuldham.

5th 1065 213 H. A. Sayles.

(C.  D. Shuldham
6th 2448 408 { and J.
( N. Muncey.

7th        4893        699            do.
8th        8912       1114            do.
9th       15129       1681            do.
10th       24160       2416        J. N. Muncey.
11th       36095       3355            do.
12th       54168       4514            do.

For further details the reader should consult the article itself, by W. S. Andrews and H. A. Sayles.

These same investigators have also performed notable feats in constructing associated and bordered prime magics, and Mr. Shuldham has sent me a remarkable paper in which he gives examples of Nasik squares constructed with primes for all orders from the 4th to the 10th, with the exception of the 3rd (which is clearly impossible) and the 9th, which, up to the time of writing, has baffled all attempts.

409.—­THE BASKETS OF PLUMS.

[Illustration]

This is the form in which I first introduced the question of magic squares with prime numbers.  I will here warn the reader that there is a little trap.

A fruit merchant had nine baskets.  Every basket contained plums (all sound and ripe), and the number in every basket was different.  When placed as shown in the illustration they formed a magic square, so that if he took any three baskets in a line in the eight possible directions there would always be the same number of plums.  This part of the puzzle is easy enough to understand.  But what follows seems at first sight a little queer.