21521911 has 4 divisors (see below), whose sum is σ = 21979872. Its totient is φ = 21063952.

The previous prime is 21521909. The next prime is 21521939. The reversal of 21521911 is 11912512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21521911 - 2¹ = 21521909 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21521971) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 228910 + ... + 229003.

It is an arithmetic number, because the mean of its divisors is an integer number (5494968).

Almost surely, 2^21521911 is an apocalyptic number.

21521911 is a deficient number, since it is larger than the sum of its proper divisors (457961).

21521911 is an equidigital number, since it uses as much as digits as its factorization.

21521911 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 457960.

The product of its digits is 180, while the sum is 22.

The square root of 21521911 is about 4639.1713699755. The cubic root of 21521911 is about 278.1593164070.

The spelling of 21521911 in words is "twenty-one million, five hundred twenty-one thousand, nine hundred eleven".