21205809849 has 8 divisors (see below), whose sum is σ = 32313615040. Its totient is φ = 12117605616.

The previous prime is 21205809839. The next prime is 21205809869. The reversal of 21205809849 is 94890850212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21205809849 - 2¹⁷ = 21205678777 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21205809798 and 21205809807.

It is not an unprimeable number, because it can be changed into a prime (21205809829) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 504900214 + ... + 504900255.

It is an arithmetic number, because the mean of its divisors is an integer number (4039201880).

Almost surely, 2^21205809849 is an apocalyptic number.

It is an amenable number.

21205809849 is a deficient number, since it is larger than the sum of its proper divisors (11107805191).

21205809849 is a wasteful number, since it uses less digits than its factorization.

21205809849 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1009800479.

The product of its (nonzero) digits is 414720, while the sum is 48.

The spelling of 21205809849 in words is "twenty-one billion, two hundred five million, eight hundred nine thousand, eight hundred forty-nine".