ADAM HART-DAVIS / SCIENCE PHOTO LIBRARY ADAM HART-DAVIS / SCIENCE PHOTO LIBRARY
Square numbers. Glass tiles laid out in a square to represent the sequence of numbers formed by the successive addition of numbers that have a common difference of 2, to a first term that is 1. Therefore, square numbers are 1 (light blue), 3 (light blue and green), 9 (light blue, green and red), 16 (light blue, green, red and dark blue) and so on.
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