Using the sieve to test primality

#sieve#primality#application

Statement

Use the sieve method to determine if $121$ is prime.

Hint

$121=11^2$ .

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Recognition. $121=11^2$ directly, so composite.

Sieve. Testing primes up to $\sqrt{121}=11$ : $2,3,5,7,11$ . $11\mid121$ , so composite.

Conclusion. $121$ is composite.