21393720 has 192 divisors, whose sum is σ = 75479040. Its totient is φ = 5443200.

The previous prime is 21393709. The next prime is 21393727. The reversal of 21393720 is 2739312.

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

It is a zygodrome in base 9.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21393727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 301285 + ... + 301355.

It is an arithmetic number, because the mean of its divisors is an integer number (393120).

Almost surely, 2^21393720 is an apocalyptic number.

21393720 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 21393720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37739520).

21393720 is an abundant number, since it is smaller than the sum of its proper divisors (54085320).

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

21393720 is a wasteful number, since it uses less digits than its factorization.

21393720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 128 (or 112 counting only the distinct ones).

The product of its (nonzero) digits is 2268, while the sum is 27.

The square root of 21393720 is about 4625.3345824924. The cubic root of 21393720 is about 277.6059493170.

The spelling of 21393720 in words is "twenty-one million, three hundred ninety-three thousand, seven hundred twenty".