20421657 has 12 divisors (see below), whose sum is σ = 29580720. Its totient is φ = 13576248.

The previous prime is 20421647. The next prime is 20421691. The reversal of 20421657 is 75612402.

20421657 is a `hidden beast` number, since 2 + 0 + 4 + 2 + 1 + 657 = 666.

It is not a de Polignac number, because 20421657 - 2⁶ = 20421593 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20421657.

It is not an unprimeable number, because it can be changed into a prime (20421647) 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, 418 + ... + 6404.

It is an arithmetic number, because the mean of its divisors is an integer number (2465060).

Almost surely, 2^20421657 is an apocalyptic number.

It is an amenable number.

20421657 is a deficient number, since it is larger than the sum of its proper divisors (9159063).

20421657 is a wasteful number, since it uses less digits than its factorization.

20421657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6372 (or 6369 counting only the distinct ones).

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

The square root of 20421657 is about 4519.0327504899. The cubic root of 20421657 is about 273.3360993507.

The spelling of 20421657 in words is "twenty million, four hundred twenty-one thousand, six hundred fifty-seven".