20421857909 has 4 divisors (see below), whose sum is σ = 20423083980. Its totient is φ = 20420631840.

The previous prime is 20421857893. The next prime is 20421857927. The reversal of 20421857909 is 90975812402.

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

It can be written as a sum of positive squares in 2 ways, for example, as 1038257284 + 19383600625 = 32222^2 + 139225^2 .

It is a cyclic number.

It is not a de Polignac number, because 20421857909 - 2⁴ = 20421857893 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 (20421857809) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 587702 + ... + 621479.

It is an arithmetic number, because the mean of its divisors is an integer number (5105770995).

Almost surely, 2^20421857909 is an apocalyptic number.

It is an amenable number.

20421857909 is a deficient number, since it is larger than the sum of its proper divisors (1226071).

20421857909 is a wasteful number, since it uses less digits than its factorization.

20421857909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1226070.

The product of its (nonzero) digits is 362880, while the sum is 47.

The spelling of 20421857909 in words is "twenty billion, four hundred twenty-one million, eight hundred fifty-seven thousand, nine hundred nine".