21015457 has 4 divisors (see below), whose sum is σ = 21024900. Its totient is φ = 21006016.

The previous prime is 21015437. The next prime is 21015461. The reversal of 21015457 is 75451012.

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 6885376 + 14130081 = 2624^2 + 3759^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21015457 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21015437) 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, 669 + ... + 6517.

It is an arithmetic number, because the mean of its divisors is an integer number (5256225).

Almost surely, 2^21015457 is an apocalyptic number.

It is an amenable number.

21015457 is a deficient number, since it is larger than the sum of its proper divisors (9443).

21015457 is an equidigital number, since it uses as much as digits as its factorization.

21015457 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9442.

The product of its (nonzero) digits is 1400, while the sum is 25.

The square root of 21015457 is about 4584.2618816992. The cubic root of 21015457 is about 275.9600910229.

Adding to 21015457 its reverse (75451012), we get a palindrome (96466469).

The spelling of 21015457 in words is "twenty-one million, fifteen thousand, four hundred fifty-seven".