21257216 has 22 divisors (see below), whose sum is σ = 42495720. Its totient is φ = 10628096.

The previous prime is 21257209. The next prime is 21257237. The reversal of 21257216 is 61275212.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9356 + ... + 11403.

Almost surely, 2^21257216 is an apocalyptic number.

It is an amenable number.

21257216 is a deficient number, since it is larger than the sum of its proper divisors (21238504).

21257216 is an equidigital number, since it uses as much as digits as its factorization.

21257216 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20779 (or 20761 counting only the distinct ones).

The product of its digits is 1680, while the sum is 26.

The square root of 21257216 is about 4610.5548473042. The cubic root of 21257216 is about 277.0142615829.

The spelling of 21257216 in words is "twenty-one million, two hundred fifty-seven thousand, two hundred sixteen".