21057215 has 16 divisors (see below), whose sum is σ = 26455296. Its totient is φ = 16070400.

The previous prime is 21057209. The next prime is 21057241. The reversal of 21057215 is 51275012.

It is a happy number.

It is not a de Polignac number, because 21057215 - 2⁴ = 21057199 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 10385 + ... + 12245.

It is an arithmetic number, because the mean of its divisors is an integer number (1653456).

Almost surely, 2^21057215 is an apocalyptic number.

21057215 is a deficient number, since it is larger than the sum of its proper divisors (5398081).

21057215 is a wasteful number, since it uses less digits than its factorization.

21057215 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1970.

The product of its (nonzero) digits is 700, while the sum is 23.

The square root of 21057215 is about 4588.8141169588. The cubic root of 21057215 is about 276.1427489180.

The spelling of 21057215 in words is "twenty-one million, fifty-seven thousand, two hundred fifteen".