21457920 has 176 divisors, whose sum is σ = 75460608. Its totient is φ = 5160960.

The previous prime is 21457871. The next prime is 21457939. The reversal of 21457920 is 2975412.

It is a tau number, because it is divible by the number of its divisors (176).

It is a Harshad number since it is a multiple of its sum of digits (30).

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, 168897 + ... + 169023.

Almost surely, 2^21457920 is an apocalyptic number.

21457920 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 21457920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37730304).

21457920 is an abundant number, since it is smaller than the sum of its proper divisors (54002688).

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

21457920 is a wasteful number, since it uses less digits than its factorization.

21457920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 166 (or 148 counting only the distinct ones).

The product of its (nonzero) digits is 5040, while the sum is 30.

The square root of 21457920 is about 4632.2694222163. The cubic root of 21457920 is about 277.8833594491.

The spelling of 21457920 in words is "twenty-one million, four hundred fifty-seven thousand, nine hundred twenty".