20939721 has 16 divisors (see below), whose sum is σ = 30621888. Its totient is φ = 12622400.

The previous prime is 20939719. The next prime is 20939731. The reversal of 20939721 is 12793902.

It is a cyclic number.

It is not a de Polignac number, because 20939721 - 2¹ = 20939719 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is not an unprimeable number, because it can be changed into a prime (20939701) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4891 + ... + 8111.

It is an arithmetic number, because the mean of its divisors is an integer number (1913868).

Almost surely, 2^20939721 is an apocalyptic number.

It is an amenable number.

20939721 is a deficient number, since it is larger than the sum of its proper divisors (9682167).

20939721 is a wasteful number, since it uses less digits than its factorization.

20939721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3432.

The product of its (nonzero) digits is 6804, while the sum is 33.

The square root of 20939721 is about 4575.9939903807. The cubic root of 20939721 is about 275.6281881666.

The spelling of 20939721 in words is "twenty million, nine hundred thirty-nine thousand, seven hundred twenty-one".