Primes / Is 21 prime?

Is 21 a Prime Number?

No21 = 3 x 7

21 is NOT prime: 3 × 7 = 21. That makes 3 a genuine divisor of 21 beyond 1 and 21 itself. Fully broken down, 21 = 3 × 7, for 4 divisors total. 21 sits between primes 19 and 23, 2 below and 2 above. 21: 3, 7 divide 21 evenly, checked against 2-12. 21 is odd, digit sum 3 for 21, digital root 3 for 21. 21 has 7 primes within 10 of 21.