21537720 has 96 divisors (see below), whose sum is σ = 72446400. Its totient is φ = 5542656.

The previous prime is 21537689. The next prime is 21537743. The reversal of 21537720 is 2773512.

It is a congruent number.

It is an unprimeable number.

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 23 ways as a sum of consecutive naturals, for example, 9409 + ... + 11471.

It is an arithmetic number, because the mean of its divisors is an integer number (754650).

Almost surely, 2^21537720 is an apocalyptic number.

21537720 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 21537720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36223200).

21537720 is an abundant number, since it is smaller than the sum of its proper divisors (50908680).

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

21537720 is a wasteful number, since it uses less digits than its factorization.

21537720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2109 (or 2102 counting only the distinct ones).

The product of its (nonzero) digits is 2940, while the sum is 27.

The square root of 21537720 is about 4640.8749175129. The cubic root of 21537720 is about 278.2274073921.

The spelling of 21537720 in words is "twenty-one million, five hundred thirty-seven thousand, seven hundred twenty".