In recreational mathematics, a square array of numbers, usually positive integers, is called a magic square if the sums of the numbers in each row, each column, and both main diagonals are the same. The 'order' of the magic square is the number of integers along one side (n), and the constant sum is called the 'magic constant'. If the array includes just the positive integers , the magic square is said to be 'normal'. Some authors take magic square to mean normal magic square.
Melencolia I (Albrecht Dürer, 1514) includes an order 4 square with magic sum 34
Iron plate with an order-6 magic square in Eastern Arabic numerals from China, dating to the Yuan Dynasty (1271–1368).
A page displaying 9×9 magic square from Cheng Dawei's Suanfa tongzong (1593).
The 3×3 magic square in different orientations forming a non-normal 6×6 magic square, from an unidentified 19th century Indian manuscript.
Encyclopedia of the Brethren of Purity
The Encyclopedia of the Brethren of Purity also variously known as the Epistles of the Brethren of Sincerity, Epistles of the Brethren of Purity and Epistles of the Brethren of Purity and Loyal Friends is an Islamic encyclopedia in 52 treatises (rasā'il) written by the mysterious Brethren of Purity of Basra, Iraq sometime in the second half of the 10th century CE. It had a great influence on later intellectual leading lights of the Muslim world, such as ibn Arabi, and was transmitted as far abroad within the Muslim world as al-Andalus.
Manuscript of the Brethren's Kitab Ikhwan al-Safa i.e. the "Epistles of the Brethren of Purity". Copy created in late Safavid Iran, dated c. 17th century
Double-leaf frontispiece from the "Encyclopedia of the Brethren of Purity". Baghdad, 1287. Süleymaniye Library (MSS Esad Efendi 3636).
Encyclopedia of the Brethren of Purity (detail). Baghdad, 1287 CE.
