21311920 has 80 divisors (see below), whose sum is σ = 59639040. Its totient is φ = 6918912.

The previous prime is 21311903. The next prime is 21311933. The reversal of 21311920 is 2911312.

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 (19).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9639 + ... + 11641.

It is an arithmetic number, because the mean of its divisors is an integer number (745488).

Almost surely, 2^21311920 is an apocalyptic number.

21311920 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21311920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29819520).

21311920 is an abundant number, since it is smaller than the sum of its proper divisors (38327120).

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

21311920 is a wasteful number, since it uses less digits than its factorization.

21311920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2042 (or 2036 counting only the distinct ones).

The product of its (nonzero) digits is 108, while the sum is 19.

The square root of 21311920 is about 4616.4835102056. The cubic root of 21311920 is about 277.2516838248.

The spelling of 21311920 in words is "twenty-one million, three hundred eleven thousand, nine hundred twenty".