21121920 has 192 divisors, whose sum is σ = 77173200. Its totient is φ = 5308416.

The previous prime is 21121913. The next prime is 21121937. The reversal of 21121920 is 2912112.

It is a tau number, because it is divible by the number of its divisors (192).

It is a super-2 number, since 2×21121920² = 892271008972800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21121893 and 21121902.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 109344 + ... + 109536.

Almost surely, 2^21121920 is an apocalyptic number.

21121920 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 21121920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38586600).

21121920 is an abundant number, since it is smaller than the sum of its proper divisors (56051280).

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

21121920 is a wasteful number, since it uses less digits than its factorization.

21121920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 237 (or 222 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 18.

The square root of 21121920 is about 4595.8590056702. The cubic root of 21121920 is about 276.4253052172.

The spelling of 21121920 in words is "twenty-one million, one hundred twenty-one thousand, nine hundred twenty".