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21125 has 12 divisors (see below), whose sum is σ = 28548. Its totient is φ = 15600.

The previous prime is 21121. The next prime is 21139. The reversal of 21125 is 52112.

Multipling 21125 by its product of digits (20), we get a square (422500 = 6502).

Adding to 21125 its reverse (52112), we get a palindrome (73237).

21125 = 152 + 162 + ... + 402.

It is a powerful number, because all its prime factors have an exponent greater than 1 and also an Achilles number because it is not a perfect power.

21125 is nontrivially palindromic in base 4.

It can be written as a sum of positive squares in 6 ways, for example, as 14884 + 6241 = 122^2 + 79^2 .

It is not a de Polignac number, because 21125 - 22 = 21121 is a prime.

It is a plaindrome in base 14.

It is a nialpdrome in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21121) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1619 + ... + 1631.

It is an arithmetic number, because the mean of its divisors is an integer number (2379).

221125 is an apocalyptic number.

21125 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21125 is a deficient number, since it is larger than the sum of its proper divisors (7423).

21125 is an equidigital number, since it uses as much as digits as its factorization.

21125 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 41 (or 18 counting only the distinct ones).

The product of its digits is 20, while the sum is 11.

The square root of 21125 is about 145.3444185375. The cubic root of 21125 is about 27.6438740684.

The spelling of 21125 in words is "twenty-one thousand, one hundred twenty-five".

Divisors: 1 5 13 25 65 125 169 325 845 1625 4225 21125