Prime Numbers
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Numbers
Compare 2 vs 21
Compare 2 vs 21
Compare
vs
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Property
2
21
Type
prime
semiprime
Unique factors
1
2
Total factors
1
2
Prime factorization
2
^{1}
3
^{1}
×
7
^{1}
Prime factorization
2
3
×
7
Divisors count
2
4
Divisors
1
,
2
1
,
3
,
7
,
21
Number of properties
26
1
Additive primes
1st
Bell primes
1st
Chen primes
1st
Class 1+ primes
1st
Dihedral primes
1st
Euclid primes
1st
Factorial primes
1st
Fibonacci primes
1st
Isolated primes
1st
Kynea primes
1st
Left-truncatable primes
1st
Lucas primes
1st
Mills primes
1st
Multiplicative primes
1st
Palindromic primes
1st
Pierpont primes
1st
Pierpont primes of the 2nd kind
1st
Primes
1st
Quartan primes
1st
Restricted left-truncatable primes
1st
Right-truncatable primes
1st
Semiprimes
7th
Sophie germain primes
1st
Thabit primes
1st
Two-sided primes
1st
Ulam primes
1st
Wedderburn-etherington primes
1st
Roman numberals
II
XXI
Base 2
10
_{2}
10101
_{2}
Base 3
2
_{3}
210
_{3}
Base 4
2
_{4}
111
_{4}
Base 5
2
_{5}
41
_{5}
Base 6
2
_{6}
33
_{6}
Base 7
2
_{7}
30
_{7}
Base 8
2
_{8}
25
_{8}
Base 9
2
_{9}
23
_{9}
Base 10
2
_{10}
21
_{10}
Base 11
2
_{11}
1a
_{11}
Base 12
2
_{12}
19
_{12}
Base 13
2
_{13}
18
_{13}
Base 14
2
_{14}
17
_{14}
Base 15
2
_{15}
16
_{15}
Base 16
2
_{16}
15
_{16}
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