21720075 has 24 divisors (see below), whose sum is σ = 38674608. Its totient is φ = 10692480.

The previous prime is 21720053. The next prime is 21720109. The reversal of 21720075 is 57002712.

It is not a de Polignac number, because 21720075 - 2⁹ = 21719563 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 10164 + ... + 12113.

It is an arithmetic number, because the mean of its divisors is an integer number (1611442).

Almost surely, 2^21720075 is an apocalyptic number.

21720075 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21720075 is a deficient number, since it is larger than the sum of its proper divisors (16954533).

21720075 is a wasteful number, since it uses less digits than its factorization.

21720075 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22303 (or 22298 counting only the distinct ones).

The product of its (nonzero) digits is 980, while the sum is 24.

The square root of 21720075 is about 4660.4801254806. The cubic root of 21720075 is about 279.0104311307.

Adding to 21720075 its reverse (57002712), we get a palindrome (78722787).

The spelling of 21720075 in words is "twenty-one million, seven hundred twenty thousand, seventy-five".