20421643 has 4 divisors (see below), whose sum is σ = 22278168. Its totient is φ = 18565120.

The previous prime is 20421629. The next prime is 20421647. The reversal of 20421643 is 34612402.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 20421643 - 2¹³ = 20413451 is a prime.

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 3 ways as a sum of consecutive naturals, for example, 928246 + ... + 928267.

It is an arithmetic number, because the mean of its divisors is an integer number (5569542).

Almost surely, 2^20421643 is an apocalyptic number.

20421643 is a deficient number, since it is larger than the sum of its proper divisors (1856525).

20421643 is a wasteful number, since it uses less digits than its factorization.

20421643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1856524.

The product of its (nonzero) digits is 1152, while the sum is 22.

The square root of 20421643 is about 4519.0312014856. The cubic root of 20421643 is about 273.3360368891.

The spelling of 20421643 in words is "twenty million, four hundred twenty-one thousand, six hundred forty-three".