21390057 has 12 divisors (see below), whose sum is σ = 33273604. Its totient is φ = 13163040.

The previous prime is 21390043. The next prime is 21390071. The reversal of 21390057 is 75009312.

It is an interprime number because it is at equal distance from previous prime (21390043) and next prime (21390071).

It can be written as a sum of positive squares in 2 ways, for example, as 5517801 + 15872256 = 2349^2 + 3984^2 .

It is not a de Polignac number, because 21390057 - 2⁴ = 21390041 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21390057.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21390007) 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, 91294 + ... + 91527.

Almost surely, 2^21390057 is an apocalyptic number.

It is an amenable number.

21390057 is a deficient number, since it is larger than the sum of its proper divisors (11883547).

21390057 is a wasteful number, since it uses less digits than its factorization.

21390057 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 182840 (or 182837 counting only the distinct ones).

The product of its (nonzero) digits is 1890, while the sum is 27.

The square root of 21390057 is about 4624.9385941870. The cubic root of 21390057 is about 277.5901046574.

Adding to 21390057 its reverse (75009312), we get a palindrome (96399369).

The spelling of 21390057 in words is "twenty-one million, three hundred ninety thousand, fifty-seven".