Mathematics - Number Theory - Divisibility and primes - Divisibility Rules and Prime Factorization

10 steps: (1) a divides b (a|b) means b/a has no remainder. 3|12 because 12/3=4. (2) DIVISIBILITY RULES: By 2: last digit even. By 3: digit sum divisible by 3. By 5: ends in 0 or 5. (3) By 4: last two digits ÷ 4. By 9: digit sum ÷ 9. By 6: divisible by both 2 and 3. (4) PRIME: exactly 2 factors (1 a