21057287 has 2 divisors, whose sum is σ = 21057288. Its totient is φ = 21057286.

The previous prime is 21057247. The next prime is 21057299. The reversal of 21057287 is 78275012.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21057287 - 2¹⁰ = 21056263 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21057247) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10528643 + 10528644.

It is an arithmetic number, because the mean of its divisors is an integer number (10528644).

Almost surely, 2^21057287 is an apocalyptic number.

21057287 is a deficient number, since it is larger than the sum of its proper divisors (1).

21057287 is an equidigital number, since it uses as much as digits as its factorization.

21057287 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 7840, while the sum is 32.

The square root of 21057287 is about 4588.8219621162. The cubic root of 21057287 is about 276.1430636518.

The spelling of 21057287 in words is "twenty-one million, fifty-seven thousand, two hundred eighty-seven".