Compare 13 vs 21

Unique factors12
Total factors12
Prime factorization13131 × 71
Prime factorization133 × 7
Divisors count24
Divisors1, 131, 3, 7, 21
Number of properties321
Centered square primes2nd 
Chen primes6th 
Cousin primes (1st member)3rd 
Cuban primes 21st 
Fibonacci primes4th 
Happy primes2nd 
Harmonic primes2nd 
Left-truncatable primes5th 
Lucky primes3rd 
Multiplicative primes5th 
Pierpont primes5th 
Prime quadruplets (2nd member)2nd 
Prime quadruplets (4th member)1st 
Prime quintuplet 1s (3rd member)1st 
Prime quintuplet 2s (2nd member)2nd 
Prime quintuplet 2s (4th member)1st 
Prime sextuplets (3rd member)1st 
Prime triplets (1st member)4th 
Prime triplets (2nd member)3rd 
Prime triplets (3rd member)2nd 
Proth primes3rd 
Pythagorean primes2nd 
Semiprimes 7th
Sexy primes (1st member)4th 
Sexy primes (2nd member)2nd 
Sexy prime triplets (2nd member)2nd 
Solinas primes5th 
Thabit primes of the 2nd kind2nd 
Twin primes (2nd member)3rd 
Ulam primes4th 
Wilson primes2nd 
Roman numberalsXIIIXXI
Base 211012101012
Base 311132103
Base 43141114
Base 5235415
Base 6216336
Base 7167307
Base 8158258
Base 9149239
Base 1013102110
Base 1112111a11
Base 1211121912
Base 1310131813
Base 14d141714
Base 15d151615
Base 16d161516
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