How Do I Do A “Facturo?” A Facturo is like a crossword puzzle, except each “clue” is a factorable number, and the “letters” are its prime factors. No guessing! 1.Factor all of the clues into primes – put them in order in the clues section 2.In the puzzle, pick an intersection of an across clue and a down clue 3.When only one prime is common to both clues: write the prime in the intersection and cross it off in both matching clue factors 4.Fill in any other primes that must fit – work your way from there / \ 9 5 / \ / / = __ x __

Factor all the “clues” into primes Primes are 2, 3, 5, 7, 11, 13, 17, 19, 23, etc (any number that can only be 1 x itself) Three easy tests for 2, 5, and 3: – 2 is the only even number prime. All other even numbers have at least one factor of 2 – All numbers ending in 0 or 5 have a factor of 5 – To see if 3 is a factor, add up a number’s digits; if that sum divides evenly by 3 then so does the number For higher primes (like 7, 11, 13, etc) use long division to see it’s a factor

Tools for breaking a number into Primes Multiplication Table – Simple products 14 = 2 x 7 12 = 2 x 6 = 2 x 2 x 3 Factor Trees – start with smaller primes 20 / \ 2 10 / \ 2 5 so 20 = 2 x 2 x 5 Shorthand Division – for dividing by 2, 3, (2 goes into 10 5 times with no remainder. 2 goes into 2 one time.) / \ (3 goes into 5 once, with 2 remainder. Carry the 2 making 1 into 21. / \ 3 goes into 21 7 times.) 3 17