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21721 = 729107
BaseRepresentation
bin101010011011001
31002210111
411103121
51143341
6244321
7120220
oct52331
932714
1021721
1115357
12106a1
139b6b
147cb7
156681
hex54d9

21721 has 8 divisors (see below), whose sum is σ = 25920. Its totient is φ = 17808.

The previous prime is 21713. The next prime is 21727. The reversal of 21721 is 12712.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21721 - 23 = 21713 is a prime.

It is a Duffinian number.

21721 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (21727) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 150 + ... + 256.

It is an arithmetic number, because the mean of its divisors is an integer number (3240).

221721 is an apocalyptic number.

It is an amenable number.

21721 is a deficient number, since it is larger than the sum of its proper divisors (4199).

21721 is a wasteful number, since it uses less digits than its factorization.

21721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 143.

The product of its digits is 28, while the sum is 13.

The square root of 21721 is about 147.3804600346. The cubic root of 21721 is about 27.9014391844.

Subtracting from 21721 its reverse (12712), we obtain a palindrome (9009).

The spelling of 21721 in words is "twenty-one thousand, seven hundred twenty-one", and thus it is an iban number.

Divisors: 1 7 29 107 203 749 3103 21721