21057731 has 2 divisors, whose sum is σ = 21057732. Its totient is φ = 21057730.

The previous prime is 21057727. The next prime is 21057763. The reversal of 21057731 is 13775012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21057731 - 2² = 21057727 is a prime.

It is a super-2 number, since 2×21057731² = 886856069736722, which contains 22 as substring.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21057731.

It is not a weakly prime, because it can be changed into another prime (21057791) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10528865 + 10528866.

It is an arithmetic number, because the mean of its divisors is an integer number (10528866).

Almost surely, 2^21057731 is an apocalyptic number.

21057731 is a deficient number, since it is larger than the sum of its proper divisors (1).

21057731 is an equidigital number, since it uses as much as digits as its factorization.

21057731 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1470, while the sum is 26.

The square root of 21057731 is about 4588.8703402907. The cubic root of 21057731 is about 276.1450044947.

The spelling of 21057731 in words is "twenty-one million, fifty-seven thousand, seven hundred thirty-one".