Prime Numbers
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Numbers
Compare 3 vs 21
Compare 3 vs 21
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Property
3
21
Type
prime
semiprime
Unique factors
1
2
Total factors
1
2
Prime factorization
3
^{1}
3
^{1}
×
7
^{1}
Prime factorization
3
3
×
7
Divisors count
2
4
Divisors
1
,
3
1
,
3
,
7
,
21
Number of properties
29
1
Additive primes
2nd
Chen primes
2nd
Class 1+ primes
2nd
Cousin primes
(1st member)
1st
Cullen primes
1st
Euclid primes
2nd
Factorial primes
2nd
Fermat primes
1st
Fibonacci primes
2nd
Left-truncatable primes
2nd
Leyland primes
1st
Lucas primes
2nd
Lucky primes
1st
Mersenne primes
1st
Multiplicative primes
2nd
Palindromic primes
2nd
Pierpont primes
2nd
Pierpont primes of the 2nd kind
2nd
Primes
2nd
Proth primes
1st
Right-truncatable primes
2nd
Semiprimes
7th
Solinas primes
1st
Sophie germain primes
2nd
Super primes
1st
Twin primes
(1st member)
1st
Two-sided primes
2nd
Ulam primes
2nd
Wagstaff primes
1st
Wedderburn-etherington primes
2nd
Roman numberals
III
XXI
Base 2
11
_{2}
10101
_{2}
Base 3
10
_{3}
210
_{3}
Base 4
3
_{4}
111
_{4}
Base 5
3
_{5}
41
_{5}
Base 6
3
_{6}
33
_{6}
Base 7
3
_{7}
30
_{7}
Base 8
3
_{8}
25
_{8}
Base 9
3
_{9}
23
_{9}
Base 10
3
_{10}
21
_{10}
Base 11
3
_{11}
1a
_{11}
Base 12
3
_{12}
19
_{12}
Base 13
3
_{13}
18
_{13}
Base 14
3
_{14}
17
_{14}
Base 15
3
_{15}
16
_{15}
Base 16
3
_{16}
15
_{16}
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