Church and bell tower of San Nicola, via Santa Maria

Facciata Chiesa di San Nicola (G. Bettini, Comune di Pisa)

The Fibonacci sequence: Leonardo Pisano, called Fibonacci, or filius Bonaccii, was one of the greatest mathematicians of the Middle Ages. Born in Pisa around 1175, son of Guglielmo Bonacci, a Pisan merchant, he began his education in the city of Bugia, near Algiers. There he became acquainted with the works of Euclid and the Arab mathematicians. Back in Pisa he presented the famous Liber aabbaci (1202), where he exhibited for the first time in Europe the Indian positional numbering, used by the Arabs. Very well-known is the Fibonacci sequence, in which each number is equal to the sum of the previous two, 0, 1, 1, 2, 3, 5, 8, 13... Recent studies, conducted by Pietro Armienti of the Department of Earth Science of the University of Pisa, have identified a relationship between the geometries of the inlay of the lunette above the original entrance portal on the façade of the church of San Nicola and the numerical sequence of the Pisan mathematician. Professor Armienti states that assuming 'as unitary the diameter of the smaller circles of the inlay, the larger ones have a double diameter, the following a triple one, while those with a diameter of 5 are divided into segments in the squares at the top of the square in which the main circle is inscribed, the central one has a diameter of 13 while the circle that circumscribes the squares in the corners has a diameter of 8. The other elements of the inlay arranged according to circular traces identify circumferences with radius 21 and 34, finally the circle that circumscribes the inlay has a diameter 55 times larger than the smaller circle. 1,2,3,5,8,13,21,34,55 are the first nine elements of the Fibonacci sequence'.