Primary school mathematics: 1234567 has three lines, the first line has 1 number, and the second and third lines have three numbers, which are equal in vertical and horizontal directions. How to arrange them? External application method 4 Add all the angles together, and you will find that the first row is used three times, and the rest of the numbers are added twice with 5 1 6, 1+2+3 ... +7 = 28, so (56+X)/5= integer, so X=4. The sum of tangent, horizontal, vertical and oblique is equal to 12 and 3 7 2, which is easy to find. The remaining six numbers are divided into three groups, and the sum of each group is equal to 8, which can only be 3 and 5, 1 and 7, 6 and 2.