21215057 has 4 divisors (see below), whose sum is σ = 21377136. Its totient is φ = 21052980.

The previous prime is 21215053. The next prime is 21215063. The reversal of 21215057 is 75051212.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21215057 - 2² = 21215053 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21215053) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 80843 + ... + 81104.

It is an arithmetic number, because the mean of its divisors is an integer number (5344284).

Almost surely, 2^21215057 is an apocalyptic number.

It is an amenable number.

21215057 is a deficient number, since it is larger than the sum of its proper divisors (162079).

21215057 is a wasteful number, since it uses less digits than its factorization.

21215057 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 162078.

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

The square root of 21215057 is about 4605.9805687823. The cubic root of 21215057 is about 276.8310081496.

Adding to 21215057 its reverse (75051212), we get a palindrome (96266269).

The spelling of 21215057 in words is "twenty-one million, two hundred fifteen thousand, fifty-seven".