21057405 has 8 divisors (see below), whose sum is σ = 33691872. Its totient is φ = 11230608.

The previous prime is 21057341. The next prime is 21057419. The reversal of 21057405 is 50475012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21057405 - 2⁶ = 21057341 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 701899 + ... + 701928.

It is an arithmetic number, because the mean of its divisors is an integer number (4211484).

Almost surely, 2^21057405 is an apocalyptic number.

It is an amenable number.

21057405 is a deficient number, since it is larger than the sum of its proper divisors (12634467).

21057405 is a wasteful number, since it uses less digits than its factorization.

21057405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1403835.

The product of its (nonzero) digits is 1400, while the sum is 24.

The square root of 21057405 is about 4588.8348194286. The cubic root of 21057405 is about 276.1435794641.

The spelling of 21057405 in words is "twenty-one million, fifty-seven thousand, four hundred five".