6 Fun Math Holidays That You Should Be Celebrating - The Average Teacher 3. Fibonacci Day Fibonacci Day takes place every year on November 23rd, because 11/23 is the first 4 digits of the Fibonacci sequence (minus 0). The Fibonacci sequence is a series of numbers where each number is the sum of the previous 2 numbers: 0, 1, 1, 2, 3, 5, 8, 13….