21585720 has 128 divisors (see below), whose sum is σ = 70943040. Its totient is φ = 5222400.

The previous prime is 21585719. The next prime is 21585743. The reversal of 21585720 is 2758512.

21585720 = 213² + 214² + ... + 420².

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

It is a zygodrome in base 9.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 157492 + ... + 157628.

Almost surely, 2^21585720 is an apocalyptic number.

21585720 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 21585720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35471520).

21585720 is an abundant number, since it is smaller than the sum of its proper divisors (49357320).

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

21585720 is a wasteful number, since it uses less digits than its factorization.

21585720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 265 (or 261 counting only the distinct ones).

The product of its (nonzero) digits is 5600, while the sum is 30.

The square root of 21585720 is about 4646.0434780574. The cubic root of 21585720 is about 278.4339443682.

The spelling of 21585720 in words is "twenty-one million, five hundred eighty-five thousand, seven hundred twenty".