21409920 has 320 divisors, whose sum is σ = 88862400. Its totient is φ = 4810752.

The previous prime is 21409909. The next prime is 21409931. The reversal of 21409920 is 2990412.

It is an interprime number because it is at equal distance from previous prime (21409909) and next prime (21409931).

It is a tau number, because it is divible by the number of its divisors (320).

It is a Harshad number since it is a multiple of its sum of digits (27).

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 362851 + ... + 362909.

It is an arithmetic number, because the mean of its divisors is an integer number (277695).

Almost surely, 2^21409920 is an apocalyptic number.

21409920 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 21409920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (44431200).

21409920 is an abundant number, since it is smaller than the sum of its proper divisors (67452480).

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

21409920 is an equidigital number, since it uses as much as digits as its factorization.

21409920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 97 (or 76 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 27.

The square root of 21409920 is about 4627.0854757612. The cubic root of 21409920 is about 277.6760023000.

The spelling of 21409920 in words is "twenty-one million, four hundred nine thousand, nine hundred twenty".