21285720 has 64 divisors (see below), whose sum is σ = 70956000. Its totient is φ = 5675904.

The previous prime is 21285709. The next prime is 21285727. The reversal of 21285720 is 2758212.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21285727) 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 15 ways as a sum of consecutive naturals, for example, 8775 + ... + 10934.

Almost surely, 2^21285720 is an apocalyptic number.

21285720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21285720 is an abundant number, since it is smaller than the sum of its proper divisors (49670280).

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

21285720 is a wasteful number, since it uses less digits than its factorization.

21285720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19729 (or 19719 counting only the distinct ones).

The product of its (nonzero) digits is 2240, while the sum is 27.

The square root of 21285720 is about 4613.6449798397. The cubic root of 21285720 is about 277.1380232874.

The spelling of 21285720 in words is "twenty-one million, two hundred eighty-five thousand, seven hundred twenty".