21205809838 has 32 divisors (see below), whose sum is σ = 33407640000. Its totient is φ = 10081424640.

The previous prime is 21205809829. The next prime is 21205809839. The reversal of 21205809838 is 83890850212.

It is a super-3 number, since 3×21205809838³ (a number of 32 digits) contains 333 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21205809839) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4317328 + ... + 4322236.

It is an arithmetic number, because the mean of its divisors is an integer number (1043988750).

Almost surely, 2^21205809838 is an apocalyptic number.

21205809838 is a deficient number, since it is larger than the sum of its proper divisors (12201830162).

21205809838 is a wasteful number, since it uses less digits than its factorization.

21205809838 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6060.

The product of its (nonzero) digits is 276480, while the sum is 46.

The spelling of 21205809838 in words is "twenty-one billion, two hundred five million, eight hundred nine thousand, eight hundred thirty-eight".