21057247 has 2 divisors, whose sum is σ = 21057248. Its totient is φ = 21057246.

The previous prime is 21057241. The next prime is 21057287. The reversal of 21057247 is 74275012.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21057247 is a prime.

It is a super-3 number, since 3×21057247³ (a number of 23 digits) contains 333 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21057241) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10528623 + 10528624.

It is an arithmetic number, because the mean of its divisors is an integer number (10528624).

Almost surely, 2^21057247 is an apocalyptic number.

21057247 is a deficient number, since it is larger than the sum of its proper divisors (1).

21057247 is an equidigital number, since it uses as much as digits as its factorization.

21057247 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3920, while the sum is 28.

The square root of 21057247 is about 4588.8176036971. The cubic root of 21057247 is about 276.1428887998.

The spelling of 21057247 in words is "twenty-one million, fifty-seven thousand, two hundred forty-seven".