21021811 has 4 divisors (see below), whose sum is σ = 21042072. Its totient is φ = 21001552.

The previous prime is 21021799. The next prime is 21021823. The reversal of 21021811 is 11812012.

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

It is an interprime number because it is at equal distance from previous prime (21021799) and next prime (21021823).

It is a cyclic number.

It is not a de Polignac number, because 21021811 - 2⁵ = 21021779 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21021851) 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, 8485 + ... + 10678.

It is an arithmetic number, because the mean of its divisors is an integer number (5260518).

Almost surely, 2^21021811 is an apocalyptic number.

21021811 is a deficient number, since it is larger than the sum of its proper divisors (20261).

21021811 is a wasteful number, since it uses less digits than its factorization.

21021811 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20260.

The product of its (nonzero) digits is 32, while the sum is 16.

The square root of 21021811 is about 4584.9548525585. The cubic root of 21021811 is about 275.9879002957.

Adding to 21021811 its reverse (11812012), we get a palindrome (32833823).

The spelling of 21021811 in words is "twenty-one million, twenty-one thousand, eight hundred eleven".