21701257 has 4 divisors (see below), whose sum is σ = 21710916. Its totient is φ = 21691600.

The previous prime is 21701243. The next prime is 21701261. The reversal of 21701257 is 75210712.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 7706176 + 13995081 = 2776^2 + 3741^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21701257 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21701297) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 507 + ... + 6607.

It is an arithmetic number, because the mean of its divisors is an integer number (5427729).

Almost surely, 2^21701257 is an apocalyptic number.

It is an amenable number.

21701257 is a deficient number, since it is larger than the sum of its proper divisors (9659).

21701257 is an equidigital number, since it uses as much as digits as its factorization.

21701257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9658.

The product of its (nonzero) digits is 980, while the sum is 25.

The square root of 21701257 is about 4658.4607973020. The cubic root of 21701257 is about 278.9298308055.

Adding to 21701257 its reverse (75210712), we get a palindrome (96911969).

The spelling of 21701257 in words is "twenty-one million, seven hundred one thousand, two hundred fifty-seven".