21000457 has 4 divisors (see below), whose sum is σ = 22235796. Its totient is φ = 19765120.

The previous prime is 21000433. The next prime is 21000461. The reversal of 21000457 is 75400012.

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 6170256 + 14830201 = 2484^2 + 3851^2 .

It is a cyclic number.

It is not a de Polignac number, because 21000457 - 2¹⁵ = 20967689 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21000407) 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, 617644 + ... + 617677.

It is an arithmetic number, because the mean of its divisors is an integer number (5558949).

Almost surely, 2^21000457 is an apocalyptic number.

It is an amenable number.

21000457 is a deficient number, since it is larger than the sum of its proper divisors (1235339).

21000457 is a wasteful number, since it uses less digits than its factorization.

21000457 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1235338.

The product of its (nonzero) digits is 280, while the sum is 19.

The square root of 21000457 is about 4582.6255574725. The cubic root of 21000457 is about 275.8944189384.

Adding to 21000457 its reverse (75400012), we get a palindrome (96400469).

The spelling of 21000457 in words is "twenty-one million, four hundred fifty-seven", and thus it is an aban number.