20645721 has 12 divisors (see below), whose sum is σ = 30784000. Its totient is φ = 13319640.

The previous prime is 20645711. The next prime is 20645749. The reversal of 20645721 is 12754602.

20645721 is a `hidden beast` number, since 206 + 457 + 2 + 1 = 666.

It is not a de Polignac number, because 20645721 - 2¹⁹ = 20121433 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20645711) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 36721 + ... + 37278.

Almost surely, 2^20645721 is an apocalyptic number.

It is an amenable number.

20645721 is a deficient number, since it is larger than the sum of its proper divisors (10138279).

20645721 is a wasteful number, since it uses less digits than its factorization.

20645721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 74036 (or 74033 counting only the distinct ones).

The product of its (nonzero) digits is 3360, while the sum is 27.

The square root of 20645721 is about 4543.7562654702. The cubic root of 20645721 is about 274.3321358139.

The spelling of 20645721 in words is "twenty million, six hundred forty-five thousand, seven hundred twenty-one".