Fibonacci first notes that square numbers can be constructed as sums of odd numbers, essentially describing an inductive construction using the formula n2 + (2n+1) = (n+1)2. Fibonacci writes:
Fibonacci unang tala na parisukat na numero ay itinayo bilang sums ng butal mga numero, na naglalarawan ng isang mahalagang pasaklaw construction gamit ang formula n 2 + (2 n +1) = (n 1) 2. Fibonacci magsusulat: