21011840 has 32 divisors (see below), whose sum is σ = 50232960. Its totient is φ = 8404480.

The previous prime is 21011839. The next prime is 21011843. The reversal of 21011840 is 4811012.

It is a tau number, because it is divible by the number of its divisors (32).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21011843) 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, 15776 + ... + 17055.

It is an arithmetic number, because the mean of its divisors is an integer number (1569780).

Almost surely, 2^21011840 is an apocalyptic number.

21011840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21011840 is an abundant number, since it is smaller than the sum of its proper divisors (29221120).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21011840 is an equidigital number, since it uses as much as digits as its factorization.

21011840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 32850 (or 32838 counting only the distinct ones).

The product of its (nonzero) digits is 64, while the sum is 17.

The square root of 21011840 is about 4583.8673628280. The cubic root of 21011840 is about 275.9442581541.

Adding to 21011840 its reverse (4811012), we get a palindrome (25822852).

The spelling of 21011840 in words is "twenty-one million, eleven thousand, eight hundred forty".