21105920 has 72 divisors (see below), whose sum is σ = 55188000. Its totient is φ = 7669760.

The previous prime is 21105913. The next prime is 21105967. The reversal of 21105920 is 2950112.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a junction number, because it is equal to n+sod(n) for n = 21105892 and 21105901.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13331 + ... + 14829.

It is an arithmetic number, because the mean of its divisors is an integer number (766500).

Almost surely, 2^21105920 is an apocalyptic number.

21105920 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 21105920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27594000).

21105920 is an abundant number, since it is smaller than the sum of its proper divisors (34082080).

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

21105920 is a wasteful number, since it uses less digits than its factorization.

21105920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1531 (or 1517 counting only the distinct ones).

The product of its (nonzero) digits is 180, while the sum is 20.

The square root of 21105920 is about 4594.1179784590. The cubic root of 21105920 is about 276.3554895609.

The spelling of 21105920 in words is "twenty-one million, one hundred five thousand, nine hundred twenty".