Is 81 a prime number?

Prime Number Checker
Number

Is 81 a prime or composite number?

Answer

Number 81 is not a Prime

81 = 3⁴

81 has 5 divisors — 1, 3, 9, 27 and 81; a prime has exactly two: 1 and itself. It is a perfect square.

Primes up to √81

9² = 81 ≤ 81 < 100 = 10², so it is enough to try primes up to 9

  • ÷2 does not divide
  • ÷3 divides

81 ÷ 3 = 27 — 3 divides 81, so 81 is composite

Nearest primes: 79 and 83

Related Calculations

See Also

Prime numbers list

NumberIs Prime
66No: 2 × 3 × 11
67Yes
68No: 2² × 17
69No: 3 × 23
70No: 2 × 5 × 7
71Yes
72No: 2³ × 3²
73Yes
74No: 2 × 37
75No: 3 × 5²
76No: 2² × 19
77No: 7 × 11
78No: 2 × 3 × 13
79Yes
80No: 2⁴ × 5
81No: 3⁴
82No: 2 × 41
83Yes
84No: 2² × 3 × 7
85No: 5 × 17
86No: 2 × 43
87No: 3 × 29
88No: 2³ × 11
89Yes
90No: 2 × 3² × 5
91No: 7 × 13
92No: 2² × 23
93No: 3 × 31
94No: 2 × 47
95No: 5 × 19

FAQ

Is 81 a prime or composite number?

Number 81 is not a Prime

How many factors are in a number 81?

5

How to check if 81 is prime?

Divide 81 by the primes in order: 9² = 81 ≤ 81 < 100 = 10², so it is enough to try primes up to 9. The first one that divides it is 3: 81 ÷ 3 = 27, so 81 is composite.

See Also