Source : "The Master Book of Mathematical Recreations" by Fred Schuh p.313-314:

The puzzle with the largest product has been borrowed from the investigations of Dr. S. Kirederf, the well-known Egyptologist and mathematician at Eugaheht, who revealed the secret of a stone found in the picturesque step pyramid at Saqqara, which was built by the famous architect Imhotep by order of the great king Zoser of the Third Dynasty in the twenty-ninth century B.C. The red granite stone, inlaid with white alabaster, gives a symbolic representation of the step pyramid ; the hieroglyphics on it mean : "Secret of Zoser, King of Upper and Lower Egypt." Since it is known that Zoser had a fervent admiration for mathematics, the inscription and the occurrence of a harp player amid the decoration representing the harmony of mathematics led Dr. Kiredef to conjecture that the mysterious symbols in the squares, which represent the stone blocks, have a mathematical meaning. After years of prolonged study, it appeared to him in that we have the original forms of our digital symbols, grouped according to the supposed solution of the puzzle of the largest product, as discussed above. This sensational discovery also showed that our decimal system was already known to the ancient Egyptians, albeit to some adepts only!

Step Pyramid of Djoser designed by Imhotep and built at least over 4500 years ago