21042257 has 4 divisors (see below), whose sum is σ = 21102900. Its totient is φ = 20981616.

The previous prime is 21042251. The next prime is 21042283. The reversal of 21042257 is 75224012.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 11282881 + 9759376 = 3359^2 + 3124^2 .

It is a cyclic number.

It is not a de Polignac number, because 21042257 - 2⁶ = 21042193 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21042251) 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, 29798 + ... + 30495.

It is an arithmetic number, because the mean of its divisors is an integer number (5275725).

Almost surely, 2^21042257 is an apocalyptic number.

It is an amenable number.

21042257 is a deficient number, since it is larger than the sum of its proper divisors (60643).

21042257 is an equidigital number, since it uses as much as digits as its factorization.

21042257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 60642.

The product of its (nonzero) digits is 1120, while the sum is 23.

The square root of 21042257 is about 4587.1839945657. The cubic root of 21042257 is about 276.0773473969.

Adding to 21042257 its reverse (75224012), we get a palindrome (96266269).

The spelling of 21042257 in words is "twenty-one million, forty-two thousand, two hundred fifty-seven".