20985721 has 8 divisors (see below), whose sum is σ = 21518784. Its totient is φ = 20457840.

The previous prime is 20985707. The next prime is 20985737. The reversal of 20985721 is 12758902.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 20985721 - 2⁷ = 20985593 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20985121) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7666 + ... + 10036.

It is an arithmetic number, because the mean of its divisors is an integer number (2689848).

Almost surely, 2^20985721 is an apocalyptic number.

It is an amenable number.

20985721 is a deficient number, since it is larger than the sum of its proper divisors (533063).

20985721 is a wasteful number, since it uses less digits than its factorization.

20985721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2591.

The product of its (nonzero) digits is 10080, while the sum is 34.

The square root of 20985721 is about 4581.0174634026. The cubic root of 20985721 is about 275.8298722246.

The spelling of 20985721 in words is "twenty million, nine hundred eighty-five thousand, seven hundred twenty-one".