21811440 has 80 divisors (see below), whose sum is σ = 77280768. Its totient is φ = 4985088.

The previous prime is 21811423. The next prime is 21811481. The reversal of 21811440 is 4411812.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (80).

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4812 + ... + 8171.

Almost surely, 2^21811440 is an apocalyptic number.

21811440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21811440 is an abundant number, since it is smaller than the sum of its proper divisors (55469328).

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

21811440 is a wasteful number, since it uses less digits than its factorization.

21811440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13006 (or 13000 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 21.

The square root of 21811440 is about 4670.2719406904. The cubic root of 21811440 is about 279.4011008651.

The spelling of 21811440 in words is "twenty-one million, eight hundred eleven thousand, four hundred forty".