20689657921 has 9 divisors (see below), whose sum is σ = 20954025379. Its totient is φ = 20428590136.

The previous prime is 20689657913. The next prime is 20689657927. The reversal of 20689657921 is 12975698602.

The square root of 20689657921 is 143839.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 9190098225 + 11499559696 = 95865^2 + 107236^2 .

It is not a de Polignac number, because 20689657921 - 2³ = 20689657913 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20689657927) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 11937771 + ... + 11939503.

Almost surely, 2^20689657921 is an apocalyptic number.

20689657921 is the 143839-th square number.

20689657921 is the 71920-th centered octagonal number.

It is an amenable number.

20689657921 is a deficient number, since it is larger than the sum of its proper divisors (264367458).

20689657921 is an frugal number, since it uses more digits than its factorization.

20689657921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3632 (or 1816 counting only the distinct ones).

The product of its (nonzero) digits is 3265920, while the sum is 55.

The spelling of 20689657921 in words is "twenty billion, six hundred eighty-nine million, six hundred fifty-seven thousand, nine hundred twenty-one".