21108257 has 8 divisors (see below), whose sum is σ = 21862440. Its totient is φ = 20367360.

The previous prime is 21108251. The next prime is 21108277. The reversal of 21108257 is 75280112.

It can be written as a sum of positive squares in 4 ways, for example, as 30976 + 21077281 = 176^2 + 4591^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 21108257 - 2²⁰ = 20059681 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21108251) 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, 32 + ... + 6497.

It is an arithmetic number, because the mean of its divisors is an integer number (2732805).

Almost surely, 2^21108257 is an apocalyptic number.

It is an amenable number.

21108257 is a deficient number, since it is larger than the sum of its proper divisors (754183).

21108257 is an equidigital number, since it uses as much as digits as its factorization.

21108257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6643.

The product of its (nonzero) digits is 1120, while the sum is 26.

The square root of 21108257 is about 4594.3723183913. The cubic root of 21108257 is about 276.3656892102.

Adding to 21108257 its reverse (75280112), we get a palindrome (96388369).

The spelling of 21108257 in words is "twenty-one million, one hundred eight thousand, two hundred fifty-seven".